diff --git a/frontend/website/src/stores/schedules.ts b/frontend/website/src/stores/schedules.ts
index 090db7c..2471d66 100644
--- a/frontend/website/src/stores/schedules.ts
+++ b/frontend/website/src/stores/schedules.ts
@@ -17,7 +17,7 @@ export const scheduleSummarySchema = z.object({
   assignmentCount: z.number().int().nonnegative(),
 })
 
-const scheduleAssignmentSchema = z.object({
+const assignmentIdentitySchema = z.object({
   id: z.number().int().positive(),
   element: z.object({
     name: z.string().min(1),
@@ -26,7 +26,11 @@ const scheduleAssignmentSchema = z.object({
   }),
 })
 
-export const assignmentForDateSchema = scheduleAssignmentSchema.extend({
+const scheduleAssignmentSchema = assignmentIdentitySchema.extend({
+  completedAt: z.string().datetime({ offset: true }).nullable(),
+})
+
+export const assignmentForDateSchema = assignmentIdentitySchema.extend({
   schedule: z.object({
     id: z.number().int().positive(),
     set: z.object({
@@ -57,6 +61,13 @@ const assignmentsForDateResponseSchema = z.object({
   assignments: z.array(assignmentForDateSchema),
 })
 
+const assignmentCompletionResponseSchema = z.object({
+  assignment: z.object({
+    id: z.number().int().positive(),
+    completedAt: z.string().datetime({ offset: true }).nullable(),
+  }),
+})
+
 const errorResponseSchema = z.object({
   error: z.string().min(1),
 })
@@ -75,6 +86,7 @@ const LIST_ERROR = "We couldn't load your schedules."
 const DETAIL_ERROR = "We couldn't load this schedule."
 const CREATE_ERROR = "We couldn't create this schedule."
 const ASSIGNMENTS_ERROR = "We couldn't load today's assignments."
+const COMPLETION_ERROR = "We couldn't update this assignment."
 
 export const useSchedulesStore = defineStore('schedules', () => {
   const schedules = ref<ScheduleSummary[]>([])
@@ -89,6 +101,8 @@ export const useSchedulesStore = defineStore('schedules', () => {
   const assignmentsForDate = ref<AssignmentForDate[]>([])
   const assignmentsLoading = ref(false)
   const assignmentsError = ref<string | null>(null)
+  const assignmentCompletionPendingIds = ref<number[]>([])
+  const assignmentCompletionErrors = ref<Record<number, string>>({})
   let activeDetailRequestId = 0
   let assignmentsRequestId = 0
 
@@ -274,6 +288,84 @@ export const useSchedulesStore = defineStore('schedules', () => {
     }
   }
 
+  async function setAssignmentCompleted(
+    assignmentId: number,
+    completed: boolean,
+  ): Promise<boolean> {
+    if (assignmentCompletionPendingIds.value.includes(assignmentId)) {
+      return false
+    }
+
+    assignmentCompletionPendingIds.value = [...assignmentCompletionPendingIds.value, assignmentId]
+    const remainingErrors = { ...assignmentCompletionErrors.value }
+    delete remainingErrors[assignmentId]
+    assignmentCompletionErrors.value = remainingErrors
+
+    try {
+      const response = await fetch(`${API_BASE}/api/assignments/${assignmentId}`, {
+        method: 'PATCH',
+        credentials: 'include',
+        headers: {
+          Accept: 'application/json',
+          'Content-Type': 'application/json',
+        },
+        body: JSON.stringify({ completed }),
+      })
+
+      if (response.status !== 200) {
+        throw new Error('assignment completion request failed')
+      }
+
+      const responseBody: unknown = await response.json()
+      const assignment = assignmentCompletionResponseSchema.parse(responseBody).assignment
+      const completionDoesNotMatchRequest = completed
+        ? assignment.completedAt === null
+        : assignment.completedAt !== null
+      if (assignment.id !== assignmentId || completionDoesNotMatchRequest) {
+        throw new Error('assignment completion response did not match request')
+      }
+
+      if (activeSchedule.value !== null) {
+        for (const day of activeSchedule.value.days) {
+          const activeAssignment = day.assignments.find(
+            (candidate) => candidate.id === assignmentId,
+          )
+          if (activeAssignment !== undefined) {
+            activeAssignment.completedAt = assignment.completedAt
+            break
+          }
+        }
+      }
+
+      if (assignment.completedAt !== null) {
+        assignmentsForDate.value = assignmentsForDate.value.filter(
+          (candidate) => candidate.id !== assignmentId,
+        )
+      }
+
+      return true
+    } catch {
+      assignmentCompletionErrors.value = {
+        ...assignmentCompletionErrors.value,
+        [assignmentId]: COMPLETION_ERROR,
+      }
+
+      return false
+    } finally {
+      assignmentCompletionPendingIds.value = assignmentCompletionPendingIds.value.filter(
+        (pendingId) => pendingId !== assignmentId,
+      )
+    }
+  }
+
+  function isAssignmentCompletionPending(assignmentId: number): boolean {
+    return assignmentCompletionPendingIds.value.includes(assignmentId)
+  }
+
+  function assignmentCompletionError(assignmentId: number): string | null {
+    return assignmentCompletionErrors.value[assignmentId] ?? null
+  }
+
   return {
     schedules,
     listLoading,
@@ -287,9 +379,14 @@ export const useSchedulesStore = defineStore('schedules', () => {
     assignmentsForDate,
     assignmentsLoading,
     assignmentsError,
+    assignmentCompletionPendingIds,
+    assignmentCompletionErrors,
     fetchSchedules,
     fetchSchedule,
     createSchedule,
     fetchAssignmentsForDate,
+    setAssignmentCompleted,
+    isAssignmentCompletionPending,
+    assignmentCompletionError,
   }
 })
diff --git a/frontend/website/src/views/DashboardView.vue b/frontend/website/src/views/DashboardView.vue
index c99ccf4..822da86 100644
--- a/frontend/website/src/views/DashboardView.vue
+++ b/frontend/website/src/views/DashboardView.vue
@@ -35,6 +35,10 @@ function formatDate(value: string): string {
     timeZone: 'UTC',
   }).format(new Date(`${value}T00:00:00Z`))
 }
+
+async function completeAssignment(assignmentId: number): Promise<void> {
+  await schedulesStore.setAssignmentCompleted(assignmentId, true)
+}
 </script>
 
 <template>
@@ -76,15 +80,19 @@ function formatDate(value: string): string {
       </p>
 
       <ul v-else class="today-assignment-list" aria-label="Today's assignments">
-        <li v-for="assignment in assignmentsForDate" :key="assignment.id">
-          <RouterLink
-            class="today-assignment-link"
-            :to="{
-              name: 'schedule-detail',
-              params: { scheduleId: assignment.schedule.id },
-            }"
-          >
-            <article class="today-assignment">
+        <li
+          v-for="assignment in assignmentsForDate"
+          :key="assignment.id"
+          :data-today-assignment="assignment.id"
+        >
+          <article class="today-assignment">
+            <RouterLink
+              class="today-assignment-link"
+              :to="{
+                name: 'schedule-detail',
+                params: { scheduleId: assignment.schedule.id },
+              }"
+            >
               <div class="today-assignment__heading">
                 <p>{{ assignment.schedule.set.name }}</p>
                 <span class="today-assignment__kind">{{ assignment.element.kind }}</span>
@@ -96,8 +104,30 @@ function formatDate(value: string): string {
                 Open schedule
                 <span aria-hidden="true">→</span>
               </span>
-            </article>
-          </RouterLink>
+            </RouterLink>
+            <div class="today-assignment__completion">
+              <p
+                v-if="schedulesStore.assignmentCompletionError(assignment.id) !== null"
+                class="assignment-completion-error"
+                role="alert"
+              >
+                {{ schedulesStore.assignmentCompletionError(assignment.id) }}
+              </p>
+              <button
+                type="button"
+                class="assignment-completion-button"
+                :aria-label="`Mark ${assignment.element.path.join(' / ')} complete`"
+                :disabled="schedulesStore.isAssignmentCompletionPending(assignment.id)"
+                @click="completeAssignment(assignment.id)"
+              >
+                {{
+                  schedulesStore.isAssignmentCompletionPending(assignment.id)
+                    ? 'Completing...'
+                    : 'Mark complete'
+                }}
+              </button>
+            </div>
+          </article>
         </li>
       </ul>
     </section>
@@ -313,12 +343,13 @@ function formatDate(value: string): string {
 
 .today-assignment-link {
   display: block;
-  height: 100%;
-  border-radius: 1rem;
+  color: inherit;
   text-decoration: none;
 }
 
 .today-assignment {
+  display: flex;
+  flex-direction: column;
   height: 100%;
   padding: 1.4rem;
   border: 1px solid rgb(24 48 41 / 12%);
@@ -330,7 +361,7 @@ function formatDate(value: string): string {
     transform 160ms ease;
 }
 
-.today-assignment-link:hover .today-assignment {
+.today-assignment:hover {
   border-color: rgb(40 92 78 / 35%);
   transform: translateY(-2px);
 }
@@ -377,6 +408,48 @@ function formatDate(value: string): string {
   font-weight: 750;
 }
 
+.today-assignment__completion {
+  display: grid;
+  justify-items: start;
+  gap: 0.65rem;
+  margin-top: auto;
+  padding-top: 1.15rem;
+  border-top: 1px solid rgb(24 48 41 / 10%);
+}
+
+.assignment-completion-button {
+  min-height: 2.5rem;
+  padding: 0.6rem 0.9rem;
+  border: 1px solid rgb(24 58 49 / 28%);
+  border-radius: 0.7rem;
+  color: #fffdf7;
+  background: #285c4e;
+  font-size: 0.78rem;
+  font-weight: 800;
+  cursor: pointer;
+}
+
+.assignment-completion-button:hover:not(:disabled) {
+  background: #183a31;
+}
+
+.assignment-completion-button:focus-visible {
+  outline: 3px solid rgb(86 127 112 / 34%);
+  outline-offset: 0.25rem;
+}
+
+.assignment-completion-button:disabled {
+  cursor: wait;
+  opacity: 0.65;
+}
+
+.assignment-completion-error {
+  margin: 0;
+  color: #9b3f32;
+  font-size: 0.76rem;
+  font-weight: 700;
+}
+
 .sets-catalog__description {
   max-width: 38rem;
   margin: 1.5rem 0 0;
diff --git a/frontend/website/src/views/ScheduleDetailView.vue b/frontend/website/src/views/ScheduleDetailView.vue
index 352f44f..9a455a9 100644
--- a/frontend/website/src/views/ScheduleDetailView.vue
+++ b/frontend/website/src/views/ScheduleDetailView.vue
@@ -39,6 +39,17 @@ function formatDate(value: string): string {
     timeZone: 'UTC',
   }).format(new Date(`${value}T00:00:00Z`))
 }
+
+function formatCompletionTime(value: string): string {
+  return new Intl.DateTimeFormat('en', {
+    dateStyle: 'medium',
+    timeStyle: 'short',
+  }).format(new Date(value))
+}
+
+async function setAssignmentCompleted(assignmentId: number, completed: boolean): Promise<void> {
+  await schedulesStore.setAssignmentCompleted(assignmentId, completed)
+}
 </script>
 
 <template>
@@ -98,9 +109,53 @@ function formatDate(value: string): string {
             <p v-if="day.assignments.length === 0" class="rest-day">Rest day</p>
 
             <ul v-else class="assignment-list">
-              <li v-for="assignment in day.assignments" :key="assignment.id">
-                <span class="assignment-path">{{ assignment.element.path.join(' / ') }}</span>
-                <span class="assignment-kind">{{ assignment.element.kind }}</span>
+              <li
+                v-for="assignment in day.assignments"
+                :key="assignment.id"
+                :class="{ 'is-completed': assignment.completedAt !== null }"
+                :data-schedule-assignment="assignment.id"
+              >
+                <div class="assignment-description">
+                  <span class="assignment-path">
+                    {{ assignment.element.path.join(' / ') }}
+                  </span>
+                  <span class="assignment-kind">{{ assignment.element.kind }}</span>
+                </div>
+                <div class="assignment-completion">
+                  <p v-if="assignment.completedAt !== null" class="assignment-completion__status">
+                    Completed
+                    <time :datetime="assignment.completedAt">
+                      {{ formatCompletionTime(assignment.completedAt) }}
+                    </time>
+                  </p>
+                  <p v-else class="assignment-completion__status">Not completed</p>
+                  <button
+                    type="button"
+                    class="assignment-completion-button"
+                    :aria-label="
+                      assignment.completedAt === null
+                        ? `Mark ${assignment.element.path.join(' / ')} complete`
+                        : `Reopen ${assignment.element.path.join(' / ')}`
+                    "
+                    :disabled="schedulesStore.isAssignmentCompletionPending(assignment.id)"
+                    @click="setAssignmentCompleted(assignment.id, assignment.completedAt === null)"
+                  >
+                    {{
+                      schedulesStore.isAssignmentCompletionPending(assignment.id)
+                        ? 'Saving...'
+                        : assignment.completedAt === null
+                          ? 'Mark complete'
+                          : 'Reopen'
+                    }}
+                  </button>
+                  <p
+                    v-if="schedulesStore.assignmentCompletionError(assignment.id) !== null"
+                    class="assignment-completion__error"
+                    role="alert"
+                  >
+                    {{ schedulesStore.assignmentCompletionError(assignment.id) }}
+                  </p>
+                </div>
               </li>
             </ul>
           </li>
@@ -223,13 +278,17 @@ h1 {
 }
 
 .assignment-list li {
-  display: flex;
-  align-items: center;
-  justify-content: space-between;
+  display: grid;
+  grid-template-columns: minmax(0, 1fr) auto;
+  align-items: start;
   gap: 1rem;
   padding: 1rem;
 }
 
+.assignment-list li.is-completed {
+  background: rgb(220 235 224 / 34%);
+}
+
 .assignment-list li + li {
   border-top: 1px solid rgb(24 48 41 / 10%);
 }
@@ -241,6 +300,14 @@ h1 {
   overflow-wrap: anywhere;
 }
 
+.assignment-description {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 1rem;
+  min-width: 0;
+}
+
 .assignment-kind {
   flex: 0 0 auto;
   padding: 0.35rem 0.55rem;
@@ -253,6 +320,68 @@ h1 {
   text-transform: none;
 }
 
+.assignment-completion {
+  display: grid;
+  justify-items: end;
+  gap: 0.55rem;
+  min-width: 12rem;
+}
+
+.assignment-completion__status,
+.assignment-completion__error {
+  margin: 0;
+  font-size: 0.74rem;
+  font-weight: 700;
+  text-align: right;
+}
+
+.assignment-completion__status {
+  color: #5e7067;
+}
+
+.assignment-completion__status time {
+  display: block;
+  margin-top: 0.2rem;
+  color: #344e45;
+}
+
+.assignment-completion__error {
+  max-width: 14rem;
+  color: #9b3f32;
+}
+
+.assignment-completion-button {
+  min-height: 2.4rem;
+  padding: 0.55rem 0.8rem;
+  border: 1px solid rgb(24 58 49 / 28%);
+  border-radius: 0.65rem;
+  color: #183a31;
+  background: #fffdf7;
+  font-size: 0.75rem;
+  font-weight: 800;
+  cursor: pointer;
+}
+
+.is-completed .assignment-completion-button {
+  color: #5e7067;
+  background: transparent;
+}
+
+.assignment-completion-button:hover:not(:disabled) {
+  border-color: #285c4e;
+  background: #f9f5e9;
+}
+
+.assignment-completion-button:focus-visible {
+  outline: 3px solid rgb(86 127 112 / 34%);
+  outline-offset: 0.25rem;
+}
+
+.assignment-completion-button:disabled {
+  cursor: wait;
+  opacity: 0.65;
+}
+
 .page-state {
   display: grid;
   min-height: 10rem;
@@ -302,7 +431,21 @@ h1 {
   }
 
   .assignment-list li {
+    grid-template-columns: 1fr;
+  }
+
+  .assignment-description {
     align-items: flex-start;
   }
+
+  .assignment-completion {
+    justify-items: start;
+    min-width: 0;
+  }
+
+  .assignment-completion__status,
+  .assignment-completion__error {
+    text-align: left;
+  }
 }
 </style>