diff --git a/common/src/errors/mod.rs b/common/src/errors/mod.rs
index 9650814..825a820 100644
--- a/common/src/errors/mod.rs
+++ b/common/src/errors/mod.rs
@@ -3,9 +3,13 @@ pub mod infallible;
 pub mod not_found;
 pub mod register_error;
 pub mod submit_result_error;
+pub mod validate_fetch_error;
+pub mod validate_submit_error;
 
 pub use fetch_tasks_error::FetchTasksError;
 pub use infallible::Infallible;
 pub use not_found::NotFound;
 pub use register_error::RegisterError;
 pub use submit_result_error::SubmitResultError;
+pub use validate_fetch_error::ValidateFetchError;
+pub use validate_submit_error::ValidateSubmitError;
diff --git a/common/src/errors/validate_fetch_error.rs b/common/src/errors/validate_fetch_error.rs
new file mode 100644
index 0000000..9fdc122
--- /dev/null
+++ b/common/src/errors/validate_fetch_error.rs
@@ -0,0 +1,8 @@
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+
+#[derive(Clone, Hash, Debug, Serialize, Deserialize, Error)]
+pub enum ValidateFetchError {
+    #[error("invalid project")]
+    InvalidProject,
+}
diff --git a/common/src/errors/validate_submit_error.rs b/common/src/errors/validate_submit_error.rs
new file mode 100644
index 0000000..1c1e8dd
--- /dev/null
+++ b/common/src/errors/validate_submit_error.rs
@@ -0,0 +1,16 @@
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+
+#[derive(Clone, Hash, Debug, Serialize, Deserialize, Error)]
+pub enum ValidateSubmitError {
+    #[error("invalid result")]
+    InvalidResult,
+    #[error("expected results for exactly one task")]
+    InvalidTaskCount,
+    #[error("the group id of all results in a group must be the first submitted result")]
+    InconsistentGroup,
+    #[error("forbidden state transition")]
+    ForbiddenStateTransition,
+    #[error("missing some results for this task")]
+    MissingResults,
+}
diff --git a/common/src/records/result.rs b/common/src/records/result.rs
index c32e590..343ee43 100644
--- a/common/src/records/result.rs
+++ b/common/src/records/result.rs
@@ -1,7 +1,7 @@
 use chrono::{DateTime, Utc};
 use serde::{Deserialize, Serialize};
 
-use crate::types::Id;
+use crate::types::{Id, ResultState};
 
 use super::Assignment;
 
@@ -13,12 +13,16 @@ pub struct Result {
     pub stdout: String,
     pub stderr: String,
     pub exit_code: Option<i32>,
+    pub group_result_id: Option<Id<Result>>,
+    pub state: ResultState,
 }
 
 #[non_exhaustive]
 #[derive(Clone, Hash, Debug, Default, Serialize, Deserialize)]
 pub struct ResultFilter {
     pub assignment_id: Option<Id<Assignment>>,
+    pub group_result_id: Option<Id<Result>>,
+    pub state: Option<ResultState>,
 }
 
 impl ResultFilter {
@@ -26,4 +30,14 @@ impl ResultFilter {
         self.assignment_id = Some(assignment_id);
         self
     }
+
+    pub fn group_result_id(mut self, group_result_id: Id<Result>) -> Self {
+        self.group_result_id = Some(group_result_id);
+        self
+    }
+
+    pub fn state(mut self, state: ResultState) -> Self {
+        self.state = Some(state);
+        self
+    }
 }
diff --git a/common/src/records/task.rs b/common/src/records/task.rs
index 385f28e..7964b9d 100644
--- a/common/src/records/task.rs
+++ b/common/src/records/task.rs
@@ -3,7 +3,7 @@ use serde::{Deserialize, Serialize};
 
 use crate::types::{Id, Interval};
 
-use super::{Project, User};
+use super::{Project, Result, User};
 
 #[derive(Clone, Hash, Debug, Serialize, Deserialize)]
 pub struct Task {
@@ -14,12 +14,15 @@ pub struct Task {
     pub stdin: String,
     pub assignments_needed: i32,
     pub assignment_user_ids: Vec<Id<User>>,
+    pub canonical_result_id: Option<Id<Result>>,
+    pub quorum: i32,
 }
 
 #[non_exhaustive]
 #[derive(Clone, Hash, Debug, Default, Serialize, Deserialize)]
 pub struct TaskFilter {
     pub project_id: Option<Id<Project>>,
+    pub canonical_result_id: Option<Id<Result>>,
 }
 
 impl TaskFilter {
@@ -27,4 +30,9 @@ impl TaskFilter {
         self.project_id = Some(project_id);
         self
     }
+
+    pub fn canonical_result_id(mut self, canonical_result_id: Id<Result>) -> Self {
+        self.canonical_result_id = Some(canonical_result_id);
+        self
+    }
 }
diff --git a/common/src/requests/mod.rs b/common/src/requests/mod.rs
index bb3d8e7..6bbfe7e 100644
--- a/common/src/requests/mod.rs
+++ b/common/src/requests/mod.rs
@@ -1,7 +1,9 @@
 pub mod fetch_tasks_request;
 pub mod register_request;
 pub mod submit_result_request;
+pub mod validate_submit_request;
 
 pub use fetch_tasks_request::FetchTasksRequest;
 pub use register_request::RegisterRequest;
 pub use submit_result_request::SubmitResultRequest;
+pub use validate_submit_request::ValidateSubmitRequest;
diff --git a/common/src/requests/validate_submit_request.rs b/common/src/requests/validate_submit_request.rs
new file mode 100644
index 0000000..9688528
--- /dev/null
+++ b/common/src/requests/validate_submit_request.rs
@@ -0,0 +1,11 @@
+use std::collections::HashMap;
+
+use serde::{Deserialize, Serialize};
+
+use crate::{records::Result, types::Id};
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct ValidateSubmitRequest {
+    // Map from result id to group id. None means error.
+    pub results: HashMap<Id<Result>, Option<Id<Result>>>,
+}
diff --git a/common/src/types/assignment_state.rs b/common/src/types/assignment_state.rs
index d5336bd..3f7338c 100644
--- a/common/src/types/assignment_state.rs
+++ b/common/src/types/assignment_state.rs
@@ -11,7 +11,4 @@ pub enum AssignmentState {
     Canceled,
     Expired,
     Submitted,
-    Valid,
-    Invalid,
-    Inconclusive,
 }
diff --git a/common/src/types/mod.rs b/common/src/types/mod.rs
index 543eb3b..16c8c8f 100644
--- a/common/src/types/mod.rs
+++ b/common/src/types/mod.rs
@@ -1,7 +1,9 @@
 pub mod assignment_state;
 pub mod id;
 pub mod interval;
+pub mod result_state;
 
 pub use assignment_state::AssignmentState;
 pub use id::Id;
 pub use interval::Interval;
+pub use result_state::ResultState;
diff --git a/common/src/types/result_state.rs b/common/src/types/result_state.rs
new file mode 100644
index 0000000..e35a76f
--- /dev/null
+++ b/common/src/types/result_state.rs
@@ -0,0 +1,15 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug, Serialize, Deserialize)]
+#[cfg_attr(feature = "sqlx", derive(sqlx::Type))]
+#[cfg_attr(
+    feature = "sqlx",
+    sqlx(type_name = "result_state", rename_all = "snake_case")
+)]
+pub enum ResultState {
+    Init,
+    Valid,
+    Invalid,
+    Inconclusive,
+    Error,
+}
diff --git a/server/.sqlx/query-0a85c57626456d79f6a57c607437b2e6b5a31199b622f28ca3692fe60eec53c9.json b/server/.sqlx/query-0a85c57626456d79f6a57c607437b2e6b5a31199b622f28ca3692fe60eec53c9.json
index ced2773..ee9c8a1 100644
--- a/server/.sqlx/query-0a85c57626456d79f6a57c607437b2e6b5a31199b622f28ca3692fe60eec53c9.json
+++ b/server/.sqlx/query-0a85c57626456d79f6a57c607437b2e6b5a31199b622f28ca3692fe60eec53c9.json
@@ -39,10 +39,7 @@
                 "init",
                 "canceled",
                 "expired",
-                "submitted",
-                "valid",
-                "invalid",
-                "inconclusive"
+                "submitted"
               ]
             }
           }
@@ -61,10 +58,7 @@
                 "init",
                 "canceled",
                 "expired",
-                "submitted",
-                "valid",
-                "invalid",
-                "inconclusive"
+                "submitted"
               ]
             }
           }
diff --git a/server/.sqlx/query-9d2127cb05e7631e969e289ff57ffd170787045c3233daad045204b9aa53f66c.json b/server/.sqlx/query-0fbc6c31fbd780f76738a14f5e0b19dac70d34e283d16169617ad59af7f04ff5.json
similarity index 52%
rename from server/.sqlx/query-9d2127cb05e7631e969e289ff57ffd170787045c3233daad045204b9aa53f66c.json
rename to server/.sqlx/query-0fbc6c31fbd780f76738a14f5e0b19dac70d34e283d16169617ad59af7f04ff5.json
index 7dbd4cf..fd66392 100644
--- a/server/.sqlx/query-9d2127cb05e7631e969e289ff57ffd170787045c3233daad045204b9aa53f66c.json
+++ b/server/.sqlx/query-0fbc6c31fbd780f76738a14f5e0b19dac70d34e283d16169617ad59af7f04ff5.json
@@ -1,6 +1,6 @@
 {
   "db_name": "PostgreSQL",
-  "query": "\n            SELECT\n                *\n            FROM\n                results\n            WHERE\n                assignment_id = $1 IS NOT FALSE\n            ",
+  "query": "\n        SELECT\n            *\n        FROM\n            results\n        WHERE\n            id = ANY($1)\n        ",
   "describe": {
     "columns": [
       {
@@ -15,28 +15,51 @@
       },
       {
         "ordinal": 2,
+        "name": "state",
+        "type_info": {
+          "Custom": {
+            "name": "result_state",
+            "kind": {
+              "Enum": [
+                "init",
+                "valid",
+                "invalid",
+                "inconclusive",
+                "error"
+              ]
+            }
+          }
+        }
+      },
+      {
+        "ordinal": 3,
         "name": "assignment_id",
         "type_info": "Int8"
       },
       {
-        "ordinal": 3,
+        "ordinal": 4,
         "name": "stdout",
         "type_info": "Text"
       },
       {
-        "ordinal": 4,
+        "ordinal": 5,
         "name": "stderr",
         "type_info": "Text"
       },
       {
-        "ordinal": 5,
+        "ordinal": 6,
         "name": "exit_code",
         "type_info": "Int4"
+      },
+      {
+        "ordinal": 7,
+        "name": "group_result_id",
+        "type_info": "Int8"
       }
     ],
     "parameters": {
       "Left": [
-        "Int8"
+        "Int8Array"
       ]
     },
     "nullable": [
@@ -45,8 +68,10 @@
       false,
       false,
       false,
+      false,
+      true,
       true
     ]
   },
-  "hash": "9d2127cb05e7631e969e289ff57ffd170787045c3233daad045204b9aa53f66c"
+  "hash": "0fbc6c31fbd780f76738a14f5e0b19dac70d34e283d16169617ad59af7f04ff5"
 }
diff --git a/server/.sqlx/query-1260e6fd3c1f30f651d1f86bf86af3351a6629a942b732ccf6740b2e683eedae.json b/server/.sqlx/query-1260e6fd3c1f30f651d1f86bf86af3351a6629a942b732ccf6740b2e683eedae.json
index 4e370e3..ffa6665 100644
--- a/server/.sqlx/query-1260e6fd3c1f30f651d1f86bf86af3351a6629a942b732ccf6740b2e683eedae.json
+++ b/server/.sqlx/query-1260e6fd3c1f30f651d1f86bf86af3351a6629a942b732ccf6740b2e683eedae.json
@@ -39,10 +39,7 @@
                 "init",
                 "canceled",
                 "expired",
-                "submitted",
-                "valid",
-                "invalid",
-                "inconclusive"
+                "submitted"
               ]
             }
           }
diff --git a/server/.sqlx/query-2daeacfdb74c4d12e2e5801d58931e6b9e29f27da54f8ed525dc71e8f3162a0a.json b/server/.sqlx/query-2daeacfdb74c4d12e2e5801d58931e6b9e29f27da54f8ed525dc71e8f3162a0a.json
index 1c1d7db..3f4340e 100644
--- a/server/.sqlx/query-2daeacfdb74c4d12e2e5801d58931e6b9e29f27da54f8ed525dc71e8f3162a0a.json
+++ b/server/.sqlx/query-2daeacfdb74c4d12e2e5801d58931e6b9e29f27da54f8ed525dc71e8f3162a0a.json
@@ -15,23 +15,46 @@
       },
       {
         "ordinal": 2,
+        "name": "state",
+        "type_info": {
+          "Custom": {
+            "name": "result_state",
+            "kind": {
+              "Enum": [
+                "init",
+                "valid",
+                "invalid",
+                "inconclusive",
+                "error"
+              ]
+            }
+          }
+        }
+      },
+      {
+        "ordinal": 3,
         "name": "assignment_id",
         "type_info": "Int8"
       },
       {
-        "ordinal": 3,
+        "ordinal": 4,
         "name": "stdout",
         "type_info": "Text"
       },
       {
-        "ordinal": 4,
+        "ordinal": 5,
         "name": "stderr",
         "type_info": "Text"
       },
       {
-        "ordinal": 5,
+        "ordinal": 6,
         "name": "exit_code",
         "type_info": "Int4"
+      },
+      {
+        "ordinal": 7,
+        "name": "group_result_id",
+        "type_info": "Int8"
       }
     ],
     "parameters": {
@@ -45,6 +68,8 @@
       false,
       false,
       false,
+      false,
+      true,
       true
     ]
   },
diff --git a/server/.sqlx/query-37247bf346c477389245f83ce58c4971bd7f593a6bcec201970fe5ae9e120e7f.json b/server/.sqlx/query-37247bf346c477389245f83ce58c4971bd7f593a6bcec201970fe5ae9e120e7f.json
new file mode 100644
index 0000000..8f8b328
--- /dev/null
+++ b/server/.sqlx/query-37247bf346c477389245f83ce58c4971bd7f593a6bcec201970fe5ae9e120e7f.json
@@ -0,0 +1,15 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n            UPDATE\n                results\n            SET\n                state = CASE\n                    WHEN group_result_id = $1 THEN 'valid'::result_state\n                    ELSE 'invalid'::result_state\n                END\n            WHERE\n                id = ANY($2)\n            ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int8",
+        "Int8Array"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "37247bf346c477389245f83ce58c4971bd7f593a6bcec201970fe5ae9e120e7f"
+}
diff --git a/server/.sqlx/query-37787d0e5dbb0fd034a68efbe9eeb11432326d631d24b5ebaea76946aa913df1.json b/server/.sqlx/query-37787d0e5dbb0fd034a68efbe9eeb11432326d631d24b5ebaea76946aa913df1.json
new file mode 100644
index 0000000..d3b1b7e
--- /dev/null
+++ b/server/.sqlx/query-37787d0e5dbb0fd034a68efbe9eeb11432326d631d24b5ebaea76946aa913df1.json
@@ -0,0 +1,70 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n        SELECT\n            t.*\n        FROM\n            tasks t\n            JOIN assignments a ON\n                a.task_id = t.id\n            LEFT JOIN results r ON\n                r.assignment_id = a.id\n                AND r.state = 'init'\n        WHERE\n            a.state = 'submitted'\n        GROUP BY\n            t.id\n        HAVING\n            t.project_id = $1\n            AND count(a.id) >= t.assignments_needed\n            AND count(r.id) > 0\n        ",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 1,
+        "name": "created_at",
+        "type_info": "Timestamptz"
+      },
+      {
+        "ordinal": 2,
+        "name": "deadline",
+        "type_info": "Interval"
+      },
+      {
+        "ordinal": 3,
+        "name": "project_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 4,
+        "name": "stdin",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 5,
+        "name": "assignments_needed",
+        "type_info": "Int4"
+      },
+      {
+        "ordinal": 6,
+        "name": "assignment_user_ids",
+        "type_info": "Int8Array"
+      },
+      {
+        "ordinal": 7,
+        "name": "canonical_result_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 8,
+        "name": "quorum",
+        "type_info": "Int4"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Int8"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      false,
+      false,
+      false,
+      false,
+      true,
+      false
+    ]
+  },
+  "hash": "37787d0e5dbb0fd034a68efbe9eeb11432326d631d24b5ebaea76946aa913df1"
+}
diff --git a/server/.sqlx/query-4f28c9855a87500c39fc4e88308b16b87bf12743e25be5d1707c07edd8d94dfd.json b/server/.sqlx/query-4f28c9855a87500c39fc4e88308b16b87bf12743e25be5d1707c07edd8d94dfd.json
index b33cd31..a86be38 100644
--- a/server/.sqlx/query-4f28c9855a87500c39fc4e88308b16b87bf12743e25be5d1707c07edd8d94dfd.json
+++ b/server/.sqlx/query-4f28c9855a87500c39fc4e88308b16b87bf12743e25be5d1707c07edd8d94dfd.json
@@ -37,6 +37,16 @@
         "ordinal": 6,
         "name": "assignment_user_ids",
         "type_info": "Int8Array"
+      },
+      {
+        "ordinal": 7,
+        "name": "canonical_result_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 8,
+        "name": "quorum",
+        "type_info": "Int4"
       }
     ],
     "parameters": {
@@ -51,6 +61,8 @@
       false,
       false,
       false,
+      false,
+      true,
       false
     ]
   },
diff --git a/server/.sqlx/query-5008175ade98bc9947127cbdfb3cfd0e1d578432b0ec081732c79d49d843abfe.json b/server/.sqlx/query-5008175ade98bc9947127cbdfb3cfd0e1d578432b0ec081732c79d49d843abfe.json
new file mode 100644
index 0000000..d052858
--- /dev/null
+++ b/server/.sqlx/query-5008175ade98bc9947127cbdfb3cfd0e1d578432b0ec081732c79d49d843abfe.json
@@ -0,0 +1,79 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n        SELECT\n            r.*\n        FROM\n            results r\n            JOIN assignments a ON\n                a.id = r.assignment_id\n        WHERE\n            a.task_id = $1\n            AND r.id < $2\n            AND r.id != ALL($3)\n        ",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 1,
+        "name": "created_at",
+        "type_info": "Timestamptz"
+      },
+      {
+        "ordinal": 2,
+        "name": "state",
+        "type_info": {
+          "Custom": {
+            "name": "result_state",
+            "kind": {
+              "Enum": [
+                "init",
+                "valid",
+                "invalid",
+                "inconclusive",
+                "error"
+              ]
+            }
+          }
+        }
+      },
+      {
+        "ordinal": 3,
+        "name": "assignment_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 4,
+        "name": "stdout",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 5,
+        "name": "stderr",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 6,
+        "name": "exit_code",
+        "type_info": "Int4"
+      },
+      {
+        "ordinal": 7,
+        "name": "group_result_id",
+        "type_info": "Int8"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Int8",
+        "Int8",
+        "Int8Array"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      false,
+      false,
+      false,
+      true,
+      true
+    ]
+  },
+  "hash": "5008175ade98bc9947127cbdfb3cfd0e1d578432b0ec081732c79d49d843abfe"
+}
diff --git a/server/.sqlx/query-758af5d6a249187a308a1746d22636256031600e6a52fc94e57880b40e306b2b.json b/server/.sqlx/query-758af5d6a249187a308a1746d22636256031600e6a52fc94e57880b40e306b2b.json
new file mode 100644
index 0000000..4facc00
--- /dev/null
+++ b/server/.sqlx/query-758af5d6a249187a308a1746d22636256031600e6a52fc94e57880b40e306b2b.json
@@ -0,0 +1,14 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n            UPDATE\n                results\n            SET\n                state = 'inconclusive'\n            WHERE\n                id = ANY($1)\n            ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int8Array"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "758af5d6a249187a308a1746d22636256031600e6a52fc94e57880b40e306b2b"
+}
diff --git a/server/.sqlx/query-8660893ff85be731039fb2402bf7c47896571f1b0b9b844e84e298f87e3ed09b.json b/server/.sqlx/query-8660893ff85be731039fb2402bf7c47896571f1b0b9b844e84e298f87e3ed09b.json
index 73ddf24..d190667 100644
--- a/server/.sqlx/query-8660893ff85be731039fb2402bf7c47896571f1b0b9b844e84e298f87e3ed09b.json
+++ b/server/.sqlx/query-8660893ff85be731039fb2402bf7c47896571f1b0b9b844e84e298f87e3ed09b.json
@@ -37,6 +37,16 @@
         "ordinal": 6,
         "name": "assignment_user_ids",
         "type_info": "Int8Array"
+      },
+      {
+        "ordinal": 7,
+        "name": "canonical_result_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 8,
+        "name": "quorum",
+        "type_info": "Int4"
       }
     ],
     "parameters": {
@@ -53,6 +63,8 @@
       false,
       false,
       false,
+      false,
+      true,
       false
     ]
   },
diff --git a/server/.sqlx/query-0d6d91c4e0acb78e4fda4df1804d430966e8ae83a168de0d3444bb8a4c7b1051.json b/server/.sqlx/query-ab022e8774fc4cef4434e9ba30b902f2e0e01a252ef1aa79e45da16db3a15fad.json
similarity index 71%
rename from server/.sqlx/query-0d6d91c4e0acb78e4fda4df1804d430966e8ae83a168de0d3444bb8a4c7b1051.json
rename to server/.sqlx/query-ab022e8774fc4cef4434e9ba30b902f2e0e01a252ef1aa79e45da16db3a15fad.json
index 8117500..73478a5 100644
--- a/server/.sqlx/query-0d6d91c4e0acb78e4fda4df1804d430966e8ae83a168de0d3444bb8a4c7b1051.json
+++ b/server/.sqlx/query-ab022e8774fc4cef4434e9ba30b902f2e0e01a252ef1aa79e45da16db3a15fad.json
@@ -1,6 +1,6 @@
 {
   "db_name": "PostgreSQL",
-  "query": "\n            SELECT\n                *\n            FROM\n                tasks\n            WHERE\n                project_id = $1 IS NOT FALSE\n            ",
+  "query": "\n            SELECT\n                *\n            FROM\n                tasks\n            WHERE\n                project_id = $1 IS NOT FALSE\n                AND (canonical_result_id = $2 OR $2 IS NULL)\n            ",
   "describe": {
     "columns": [
       {
@@ -37,10 +37,21 @@
         "ordinal": 6,
         "name": "assignment_user_ids",
         "type_info": "Int8Array"
+      },
+      {
+        "ordinal": 7,
+        "name": "canonical_result_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 8,
+        "name": "quorum",
+        "type_info": "Int4"
       }
     ],
     "parameters": {
       "Left": [
+        "Int8",
         "Int8"
       ]
     },
@@ -51,8 +62,10 @@
       false,
       false,
       false,
+      false,
+      true,
       false
     ]
   },
-  "hash": "0d6d91c4e0acb78e4fda4df1804d430966e8ae83a168de0d3444bb8a4c7b1051"
+  "hash": "ab022e8774fc4cef4434e9ba30b902f2e0e01a252ef1aa79e45da16db3a15fad"
 }
diff --git a/server/.sqlx/query-bf6f3f4b26b32f1f446cf0fd67c462cd94a548cd83fbc39fb826ced7c0bce9f1.json b/server/.sqlx/query-bf6f3f4b26b32f1f446cf0fd67c462cd94a548cd83fbc39fb826ced7c0bce9f1.json
new file mode 100644
index 0000000..f98d975
--- /dev/null
+++ b/server/.sqlx/query-bf6f3f4b26b32f1f446cf0fd67c462cd94a548cd83fbc39fb826ced7c0bce9f1.json
@@ -0,0 +1,28 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n        UPDATE \n            results\n        SET \n            state = $1\n        WHERE\n            id = ANY($2)\n        ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        {
+          "Custom": {
+            "name": "result_state",
+            "kind": {
+              "Enum": [
+                "init",
+                "valid",
+                "invalid",
+                "inconclusive",
+                "error"
+              ]
+            }
+          }
+        },
+        "Int8Array"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "bf6f3f4b26b32f1f446cf0fd67c462cd94a548cd83fbc39fb826ced7c0bce9f1"
+}
diff --git a/server/.sqlx/query-cd5ffd3d5d60bb7c7072db520c4d1c9875f8443a0982e81d1538161656074183.json b/server/.sqlx/query-cd5ffd3d5d60bb7c7072db520c4d1c9875f8443a0982e81d1538161656074183.json
new file mode 100644
index 0000000..9ea0108
--- /dev/null
+++ b/server/.sqlx/query-cd5ffd3d5d60bb7c7072db520c4d1c9875f8443a0982e81d1538161656074183.json
@@ -0,0 +1,70 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n        SELECT\n            t.*\n        FROM\n            tasks t\n            JOIN assignments a ON\n                a.task_id = t.id\n        WHERE\n            a.id = ANY($1)\n        ",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 1,
+        "name": "created_at",
+        "type_info": "Timestamptz"
+      },
+      {
+        "ordinal": 2,
+        "name": "deadline",
+        "type_info": "Interval"
+      },
+      {
+        "ordinal": 3,
+        "name": "project_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 4,
+        "name": "stdin",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 5,
+        "name": "assignments_needed",
+        "type_info": "Int4"
+      },
+      {
+        "ordinal": 6,
+        "name": "assignment_user_ids",
+        "type_info": "Int8Array"
+      },
+      {
+        "ordinal": 7,
+        "name": "canonical_result_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 8,
+        "name": "quorum",
+        "type_info": "Int4"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Int8Array"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      false,
+      false,
+      false,
+      false,
+      true,
+      false
+    ]
+  },
+  "hash": "cd5ffd3d5d60bb7c7072db520c4d1c9875f8443a0982e81d1538161656074183"
+}
diff --git a/server/.sqlx/query-ce2921487afc54738ea394ab248c5602d215db4e5cf61484cf7b80c84b0cfe5c.json b/server/.sqlx/query-ce2921487afc54738ea394ab248c5602d215db4e5cf61484cf7b80c84b0cfe5c.json
index c49c6dc..e351a95 100644
--- a/server/.sqlx/query-ce2921487afc54738ea394ab248c5602d215db4e5cf61484cf7b80c84b0cfe5c.json
+++ b/server/.sqlx/query-ce2921487afc54738ea394ab248c5602d215db4e5cf61484cf7b80c84b0cfe5c.json
@@ -39,10 +39,7 @@
                 "init",
                 "canceled",
                 "expired",
-                "submitted",
-                "valid",
-                "invalid",
-                "inconclusive"
+                "submitted"
               ]
             }
           }
diff --git a/server/.sqlx/query-d3f83d3bf9b010cdf4a5c8c65b2faf7ba6f659832bd727aa8faa69fe761254d1.json b/server/.sqlx/query-d3f83d3bf9b010cdf4a5c8c65b2faf7ba6f659832bd727aa8faa69fe761254d1.json
index 67cb28d..78957cc 100644
--- a/server/.sqlx/query-d3f83d3bf9b010cdf4a5c8c65b2faf7ba6f659832bd727aa8faa69fe761254d1.json
+++ b/server/.sqlx/query-d3f83d3bf9b010cdf4a5c8c65b2faf7ba6f659832bd727aa8faa69fe761254d1.json
@@ -13,10 +13,7 @@
                 "init",
                 "canceled",
                 "expired",
-                "submitted",
-                "valid",
-                "invalid",
-                "inconclusive"
+                "submitted"
               ]
             }
           }
diff --git a/server/.sqlx/query-d87fa0f565013412bab63b399f7dd435b8f6ef317eec2981cf24b97d9a1394ed.json b/server/.sqlx/query-d87fa0f565013412bab63b399f7dd435b8f6ef317eec2981cf24b97d9a1394ed.json
new file mode 100644
index 0000000..b16c3f7
--- /dev/null
+++ b/server/.sqlx/query-d87fa0f565013412bab63b399f7dd435b8f6ef317eec2981cf24b97d9a1394ed.json
@@ -0,0 +1,92 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n            SELECT\n                *\n            FROM\n                results\n            WHERE\n                assignment_id = $1 IS NOT FALSE\n                AND (group_result_id = $2 OR $2 IS NULL)\n                AND state = $3 IS NOT FALSE\n            ",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 1,
+        "name": "created_at",
+        "type_info": "Timestamptz"
+      },
+      {
+        "ordinal": 2,
+        "name": "state",
+        "type_info": {
+          "Custom": {
+            "name": "result_state",
+            "kind": {
+              "Enum": [
+                "init",
+                "valid",
+                "invalid",
+                "inconclusive",
+                "error"
+              ]
+            }
+          }
+        }
+      },
+      {
+        "ordinal": 3,
+        "name": "assignment_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 4,
+        "name": "stdout",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 5,
+        "name": "stderr",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 6,
+        "name": "exit_code",
+        "type_info": "Int4"
+      },
+      {
+        "ordinal": 7,
+        "name": "group_result_id",
+        "type_info": "Int8"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Int8",
+        "Int8",
+        {
+          "Custom": {
+            "name": "result_state",
+            "kind": {
+              "Enum": [
+                "init",
+                "valid",
+                "invalid",
+                "inconclusive",
+                "error"
+              ]
+            }
+          }
+        }
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      false,
+      false,
+      false,
+      true,
+      true
+    ]
+  },
+  "hash": "d87fa0f565013412bab63b399f7dd435b8f6ef317eec2981cf24b97d9a1394ed"
+}
diff --git a/server/.sqlx/query-dd2ccc411586e044836d4f5c9d3dad562d8eecde82db258dc183868b211f4410.json b/server/.sqlx/query-dd2ccc411586e044836d4f5c9d3dad562d8eecde82db258dc183868b211f4410.json
new file mode 100644
index 0000000..4a4102a
--- /dev/null
+++ b/server/.sqlx/query-dd2ccc411586e044836d4f5c9d3dad562d8eecde82db258dc183868b211f4410.json
@@ -0,0 +1,15 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n                UPDATE\n                    results\n                SET\n                    group_result_id = $1\n                WHERE\n                    id = $2\n                ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int8",
+        "Int8"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "dd2ccc411586e044836d4f5c9d3dad562d8eecde82db258dc183868b211f4410"
+}
diff --git a/server/.sqlx/query-f0f7b39962dd47d3a523564bbe52e6fd3fabcc164935906cd974dabd677ec14f.json b/server/.sqlx/query-f0f7b39962dd47d3a523564bbe52e6fd3fabcc164935906cd974dabd677ec14f.json
new file mode 100644
index 0000000..5b8d773
--- /dev/null
+++ b/server/.sqlx/query-f0f7b39962dd47d3a523564bbe52e6fd3fabcc164935906cd974dabd677ec14f.json
@@ -0,0 +1,15 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n            UPDATE\n                tasks\n            SET\n                assignments_needed = $1\n            WHERE\n                id = $2\n            ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int4",
+        "Int8"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "f0f7b39962dd47d3a523564bbe52e6fd3fabcc164935906cd974dabd677ec14f"
+}
diff --git a/server/.sqlx/query-f7b43273fca1553daea58cb93f9b829c0a9d46d6dc4aa18e76f9fd309e207d54.json b/server/.sqlx/query-f7b43273fca1553daea58cb93f9b829c0a9d46d6dc4aa18e76f9fd309e207d54.json
new file mode 100644
index 0000000..6cdadc0
--- /dev/null
+++ b/server/.sqlx/query-f7b43273fca1553daea58cb93f9b829c0a9d46d6dc4aa18e76f9fd309e207d54.json
@@ -0,0 +1,40 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n        SELECT\n            *\n        FROM\n            projects\n        WHERE\n            id = $1\n        ",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 1,
+        "name": "created_at",
+        "type_info": "Timestamptz"
+      },
+      {
+        "ordinal": 2,
+        "name": "disabled_at",
+        "type_info": "Timestamptz"
+      },
+      {
+        "ordinal": 3,
+        "name": "name",
+        "type_info": "Text"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Int8"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      true,
+      false
+    ]
+  },
+  "hash": "f7b43273fca1553daea58cb93f9b829c0a9d46d6dc4aa18e76f9fd309e207d54"
+}
diff --git a/server/migrations/20250426220809_init.sql b/server/migrations/20250426220809_init.sql
index 7088a1a..2ef73e5 100644
--- a/server/migrations/20250426220809_init.sql
+++ b/server/migrations/20250426220809_init.sql
@@ -38,17 +38,16 @@ CREATE TABLE tasks (
     project_id int8 NOT NULL REFERENCES projects(id) ON DELETE RESTRICT ON UPDATE RESTRICT,
     stdin text NOT NULL,
     assignments_needed int4 NOT NULL,
-    assignment_user_ids int8[] NOT NULL DEFAULT ARRAY[]::int8[]
+    assignment_user_ids int8[] NOT NULL DEFAULT ARRAY[]::int8[],
+    canonical_result_id int8,
+    quorum int4 NOT NULL
 );
 
 CREATE TYPE assignment_state AS ENUM (
-    'init', 
-    'canceled', 
+    'init',
+    'canceled',
     'expired',
-    'submitted', 
-    'valid', 
-    'invalid',  
-    'inconclusive'
+    'submitted'
 );
 
 CREATE TABLE assignments (
@@ -64,15 +63,28 @@ CREATE UNIQUE INDEX assignments_task_id_user_id_key
     ON assignments (task_id, user_id)
     WHERE state != 'canceled' AND state != 'expired';
 
+CREATE TYPE result_state AS ENUM (
+    'init',
+    'valid',
+    'invalid',
+    'inconclusive',
+    'error'
+);
+
 CREATE TABLE results (
     id int8 GENERATED ALWAYS AS IDENTITY NOT NULL PRIMARY KEY,
     created_at timestamptz NOT NULL DEFAULT now(),
+    state result_state NOT NULL DEFAULT 'init',
     assignment_id int8 NOT NULL UNIQUE REFERENCES assignments(id) ON DELETE RESTRICT ON UPDATE RESTRICT,
     stdout text NOT NULL,
     stderr text NOT NULL,
-    exit_code int4
+    exit_code int4,
+    group_result_id int8 REFERENCES results(id) ON DELETE RESTRICT ON UPDATE RESTRICT
 );
 
+ALTER TABLE tasks
+ADD FOREIGN KEY (canonical_result_id) REFERENCES results(id) ON DELETE RESTRICT ON UPDATE RESTRICT;
+
 CREATE FUNCTION trigger_function_tasks_remove_assignment_user_id()
     RETURNS TRIGGER AS $$
 BEGIN
diff --git a/server/src/main.rs b/server/src/main.rs
index 91368df..1aa9526 100644
--- a/server/src/main.rs
+++ b/server/src/main.rs
@@ -13,6 +13,7 @@ use axum::{
 use clusterizer_common::records::{
     Assignment, Platform, Project, ProjectVersion, Result, Task, User,
 };
+
 use routes::{get_all, get_one};
 use sqlx::PgPool;
 use state::AppState;
@@ -57,6 +58,8 @@ async fn serve_task(state: AppState, address: String) {
         .route("/register", post(routes::register))
         .route("/fetch_tasks", post(routes::fetch_tasks))
         .route("/submit_result/{id}", post(routes::submit_result))
+        .route("/validate_fetch/{id}", get(routes::validate_fetch))
+        .route("/validate_submit", post(routes::validate_submit))
         .layer(TraceLayer::new_for_http())
         .with_state(state);
 
diff --git a/server/src/result/status.rs b/server/src/result/status.rs
index d41991c..15b5baa 100644
--- a/server/src/result/status.rs
+++ b/server/src/result/status.rs
@@ -1,6 +1,7 @@
 use axum::http::StatusCode;
 use clusterizer_common::errors::{
-    FetchTasksError, Infallible, NotFound, RegisterError, SubmitResultError,
+    FetchTasksError, Infallible, NotFound, RegisterError, SubmitResultError, ValidateFetchError,
+    ValidateSubmitError,
 };
 
 pub trait Status {
@@ -36,3 +37,15 @@ impl Status for SubmitResultError {
         StatusCode::BAD_REQUEST
     }
 }
+
+impl Status for ValidateSubmitError {
+    fn status(&self) -> StatusCode {
+        StatusCode::BAD_REQUEST
+    }
+}
+
+impl Status for ValidateFetchError {
+    fn status(&self) -> StatusCode {
+        StatusCode::BAD_REQUEST
+    }
+}
diff --git a/server/src/routes/fetch_tasks.rs b/server/src/routes/fetch_tasks.rs
index d75b28f..03d346e 100644
--- a/server/src/routes/fetch_tasks.rs
+++ b/server/src/routes/fetch_tasks.rs
@@ -28,7 +28,7 @@ pub async fn fetch_tasks(
         WHERE
             id = ANY($1)
         "#,
-        request.project_ids
+        request.project_ids,
     )
     .fetch_all(&mut *tx)
     .await?;
diff --git a/server/src/routes/mod.rs b/server/src/routes/mod.rs
index 511e0bc..2bdf9e2 100644
--- a/server/src/routes/mod.rs
+++ b/server/src/routes/mod.rs
@@ -16,10 +16,14 @@ use crate::{
 pub mod fetch_tasks;
 pub mod register;
 pub mod submit_result;
+pub mod validate_fetch;
+pub mod validate_submit;
 
 pub use fetch_tasks::fetch_tasks;
 pub use register::register;
 pub use submit_result::submit_result;
+pub use validate_fetch::validate_fetch;
+pub use validate_submit::validate_submit;
 
 pub async fn get_all<T: Select + Send + Unpin>(
     State(state): State<AppState>,
diff --git a/server/src/routes/validate_fetch.rs b/server/src/routes/validate_fetch.rs
new file mode 100644
index 0000000..dd99c0a
--- /dev/null
+++ b/server/src/routes/validate_fetch.rs
@@ -0,0 +1,63 @@
+use axum::{
+    Json,
+    extract::{Path, State},
+};
+use clusterizer_common::{
+    errors::ValidateFetchError,
+    records::{Project, Task},
+    types::Id,
+};
+
+use crate::{
+    result::{AppResult, ResultExt},
+    state::AppState,
+};
+
+pub async fn validate_fetch(
+    State(state): State<AppState>,
+    Path(project_id): Path<Id<Project>>,
+) -> AppResult<Json<Vec<Task>>, ValidateFetchError> {
+    let project = sqlx::query_as_unchecked!(
+        Project,
+        r#"
+        SELECT
+            *
+        FROM
+            projects
+        WHERE
+            id = $1
+        "#,
+        project_id,
+    )
+    .fetch_one(&state.pool)
+    .await
+    .map_not_found(ValidateFetchError::InvalidProject)?;
+
+    let tasks = sqlx::query_as_unchecked!(
+        Task,
+        r#"
+        SELECT
+            t.*
+        FROM
+            tasks t
+            JOIN assignments a ON
+                a.task_id = t.id
+            LEFT JOIN results r ON
+                r.assignment_id = a.id
+                AND r.state = 'init'
+        WHERE
+            a.state = 'submitted'
+        GROUP BY
+            t.id
+        HAVING
+            t.project_id = $1
+            AND count(a.id) >= t.assignments_needed
+            AND count(r.id) > 0
+        "#,
+        project.id,
+    )
+    .fetch_all(&state.pool)
+    .await?;
+
+    Ok(Json(tasks))
+}
diff --git a/server/src/routes/validate_submit.rs b/server/src/routes/validate_submit.rs
new file mode 100644
index 0000000..bf9d260
--- /dev/null
+++ b/server/src/routes/validate_submit.rs
@@ -0,0 +1,248 @@
+use axum::{Json, extract::State};
+use clusterizer_common::{
+    errors::ValidateSubmitError,
+    records::{Result, Task},
+    requests::ValidateSubmitRequest,
+    types::ResultState,
+};
+
+use std::collections::HashMap;
+
+use crate::{
+    result::{AppError, AppResult},
+    state::AppState,
+    util::set_result_state,
+};
+
+pub async fn validate_submit(
+    State(state): State<AppState>,
+    Json(request): Json<ValidateSubmitRequest>,
+) -> AppResult<(), ValidateSubmitError> {
+    // Fetch results from the request.
+    let result_ids: Vec<_> = request.results.keys().collect();
+
+    let results = sqlx::query_as_unchecked!(
+        Result,
+        r#"
+        SELECT
+            *
+        FROM
+            results
+        WHERE
+            id = ANY($1)
+        "#,
+        result_ids
+    )
+    .fetch_all(&state.pool)
+    .await?;
+
+    // Check all result ids were valid.
+    if results.len() != request.results.len() {
+        Err(AppError::Specific(ValidateSubmitError::InvalidResult))?
+    }
+
+    // Check all results have the 'init' state.
+    if results
+        .iter()
+        .any(|result| result.state != ResultState::Init)
+    {
+        Err(AppError::Specific(
+            ValidateSubmitError::ForbiddenStateTransition,
+        ))?
+    }
+
+    // Fetch tasks for the results we are going to validate.
+    let assignment_ids: Vec<_> = results.iter().map(|result| result.assignment_id).collect();
+
+    let tasks = sqlx::query_as_unchecked!(
+        Task,
+        r#"
+        SELECT
+            t.*
+        FROM
+            tasks t
+            JOIN assignments a ON
+                a.task_id = t.id
+        WHERE
+            a.id = ANY($1)
+        "#,
+        assignment_ids,
+    )
+    .fetch_all(&state.pool)
+    .await?;
+
+    // Can only validate one task at a time, for now.
+    if tasks.len() != 1 {
+        Err(AppError::Specific(ValidateSubmitError::InvalidTaskCount))?
+    }
+
+    let task = &tasks[0];
+
+    // Fetch the remaining results for this task. This ignores results whose id exceeds the largest
+    // id from the validation request, because the validator program also did not consider them.
+    let last_result_id = request
+        .results
+        .keys()
+        .max()
+        .expect("results cannot be empty");
+
+    let previous_results = sqlx::query_as_unchecked!(
+        Result,
+        r#"
+        SELECT
+            r.*
+        FROM
+            results r
+            JOIN assignments a ON
+                a.id = r.assignment_id
+        WHERE
+            a.task_id = $1
+            AND r.id < $2
+            AND r.id != ALL($3)
+        "#,
+        task.id,
+        last_result_id,
+        result_ids,
+    )
+    .fetch_all(&state.pool)
+    .await?;
+
+    // Check the validator didn't miss any tasks. This is needed for deterministic validation.
+    if previous_results
+        .iter()
+        .any(|result| result.state == ResultState::Init)
+    {
+        Err(AppError::Specific(ValidateSubmitError::MissingResults))?
+    }
+
+    // Build groups and errored results.
+    let mut groups: HashMap<_, Vec<_>> = HashMap::new();
+    let mut error_result_ids = Vec::new();
+
+    for result in &previous_results {
+        if let Some(group_id) = result.group_result_id {
+            groups.entry(group_id).or_default().push(result.id);
+        }
+    }
+
+    for (&result_id, &group_id) in &request.results {
+        if let Some(group_id) = group_id {
+            groups.entry(group_id).or_default().push(result_id);
+        } else {
+            error_result_ids.push(result_id);
+        }
+    }
+
+    // Check that each group id is the lowest of any result ids in the group.
+    for (group_id, result_ids) in &groups {
+        if group_id != result_ids.iter().min().expect("group cannot be empty") {
+            Err(AppError::Specific(ValidateSubmitError::InconsistentGroup))?
+        }
+    }
+
+    // Update state of error results.
+    set_result_state(&error_result_ids, ResultState::Error)
+        .execute(&state.pool)
+        .await?;
+
+    // Update group ids.
+    for (&result_id, &group_id) in &request.results {
+        if let Some(group_id) = group_id {
+            sqlx::query_unchecked!(
+                r#"
+                UPDATE
+                    results
+                SET
+                    group_result_id = $1
+                WHERE
+                    id = $2
+                "#,
+                group_id,
+                result_id,
+            )
+            .execute(&state.pool)
+            .await?;
+        }
+    }
+
+    // Find the id of a group that meets quorum, if any. When multiple groups meet quorum, we
+    // select the one with the lowest id instead of the largest group. This is needed for
+    // deterministic validation.
+    let valid_group_id = groups
+        .iter()
+        .filter(|(_, results)| results.len() as i32 >= task.quorum)
+        .map(|(&group_id, _)| group_id)
+        .min();
+
+    if let Some(valid_group_id) = valid_group_id {
+        // If there was a valid group, update the state of all results.
+        let group_result_ids: Vec<_> = groups.values().flatten().collect();
+
+        sqlx::query_unchecked!(
+            r#"
+            UPDATE
+                results
+            SET
+                state = CASE
+                    WHEN group_result_id = $1 THEN 'valid'::result_state
+                    ELSE 'invalid'::result_state
+                END
+            WHERE
+                id = ANY($2)
+            "#,
+            valid_group_id,
+            group_result_ids,
+        )
+        .execute(&state.pool)
+        .await?;
+    } else {
+        // Otherwise, update the state of the new results to 'inconclusive'.
+        let inconclusive_result_ids: Vec<_> = request
+            .results
+            .iter()
+            .filter(|(_, group_id)| group_id.is_some())
+            .map(|(result_id, _)| result_id)
+            .collect();
+
+        sqlx::query_unchecked!(
+            r#"
+            UPDATE
+                results
+            SET
+                state = 'inconclusive'
+            WHERE
+                id = ANY($1)
+            "#,
+            inconclusive_result_ids,
+        )
+        .execute(&state.pool)
+        .await?;
+
+        // Finally, update the number of assignments needed.
+        let largest_inconclusive_group = groups
+            .values()
+            .max_by_key(|results| results.len())
+            .expect("there is at least one group");
+
+        let assignments_needed = (results.len() + previous_results.len()
+            - largest_inconclusive_group.len()) as i32
+            + task.quorum;
+
+        sqlx::query_unchecked!(
+            r#"
+            UPDATE
+                tasks
+            SET
+                assignments_needed = $1
+            WHERE
+                id = $2
+            "#,
+            assignments_needed,
+            task.id,
+        )
+        .execute(&state.pool)
+        .await?;
+    }
+
+    Ok(())
+}
diff --git a/server/src/util/mod.rs b/server/src/util/mod.rs
index b1c2080..4c2d0bb 100644
--- a/server/src/util/mod.rs
+++ b/server/src/util/mod.rs
@@ -6,10 +6,12 @@ use sqlx::{
 pub mod assignment_deadline;
 pub mod select;
 pub mod set_assignment_state;
+pub mod set_result_state;
 
 pub use assignment_deadline::update_expired_assignments;
 pub use select::Select;
 pub use set_assignment_state::set_assignment_state;
+pub use set_result_state::set_result_state;
 
 type Query = sqlx::query::Query<'static, Postgres, PgArguments>;
 type QueryScalar<T> = sqlx::query::QueryScalar<'static, Postgres, T, PgArguments>;
diff --git a/server/src/util/select.rs b/server/src/util/select.rs
index 755692c..43a500b 100644
--- a/server/src/util/select.rs
+++ b/server/src/util/select.rs
@@ -122,8 +122,10 @@ impl Select for Task {
                 tasks
             WHERE
                 project_id = $1 IS NOT FALSE
+                AND (canonical_result_id = $2 OR $2 IS NULL)
             "#,
             filter.project_id,
+            filter.canonical_result_id,
         )
     }
 
@@ -172,8 +174,12 @@ impl Select for Result {
                 results
             WHERE
                 assignment_id = $1 IS NOT FALSE
+                AND (group_result_id = $2 OR $2 IS NULL)
+                AND state = $3 IS NOT FALSE
             "#,
             filter.assignment_id,
+            filter.group_result_id,
+            filter.state,
         )
     }
 
diff --git a/server/src/util/set_assignment_state.rs b/server/src/util/set_assignment_state.rs
index aeb1c3f..54d891c 100644
--- a/server/src/util/set_assignment_state.rs
+++ b/server/src/util/set_assignment_state.rs
@@ -19,6 +19,6 @@ pub fn set_assignment_state(
             id = ANY($2)
         "#,
         assignment_state,
-        assignment_ids
+        assignment_ids,
     )
 }
diff --git a/server/src/util/set_result_state.rs b/server/src/util/set_result_state.rs
new file mode 100644
index 0000000..75cdf49
--- /dev/null
+++ b/server/src/util/set_result_state.rs
@@ -0,0 +1,21 @@
+use clusterizer_common::{
+    records::Result,
+    types::{Id, ResultState},
+};
+
+use super::Query;
+
+pub fn set_result_state(result_ids: &[Id<Result>], result_state: ResultState) -> Query {
+    sqlx::query_unchecked!(
+        r#"
+        UPDATE 
+            results
+        SET 
+            state = $1
+        WHERE
+            id = ANY($2)
+        "#,
+        result_state,
+        result_ids,
+    )
+}