diff --git a/atlas/templates/atlas/collection_detail.html b/atlas/templates/atlas/collection_detail.html
index 6275710f..0efb370d 100644
--- a/atlas/templates/atlas/collection_detail.html
+++ b/atlas/templates/atlas/collection_detail.html
@@ -4,30 +4,30 @@
 
 {% partialdef casedetails-management-links %}
 
-                (<a href="{% url 'atlas:collection_case_displaysetup' casedetail.collection.pk casedetail.case.pk %}"><i class="bi bi-display" title="Setup default display"></i></a>
+    (<a href="{% url 'atlas:collection_case_displaysetup' casedetail.collection.pk casedetail.case.pk %}"><i class="bi bi-display" title="Setup default display"></i></a>
 
-                {% if casedetail.default_viewerstate %}
-                    <i class="bi bi-check text-success" title="This case has a default viewerstate defined"></i>
-                {% endif %}
-                )
+    {% if casedetail.default_viewerstate %}
+        <i class="bi bi-check text-success" title="This case has a default viewerstate defined"></i>
+    {% endif %}
+    )
 
-                (<a href="{% url 'atlas:collection_case_details' casedetail.collection.pk casedetail.case.pk %}"><i class="bi bi-info-square" title="Case details"></i></a>)
+    (<a href="{% url 'atlas:collection_case_details' casedetail.collection.pk casedetail.case.pk %}"><i class="bi bi-info-square" title="Case details"></i></a>)
 
-                {% if collection.collection_type == "QUE" %}
-                    (<a href='{% url "atlas:collection_case_questions" casedetail.collection.pk casedetail.case.pk %}'>
-                        {% if casedetail.question_schema %}
-                            <i class="bi bi-question-square text-success" title="This case has questions defined."></i>
-                        {% else %}
-                            <i class="bi bi-question-square text-danger" title="This case has no questions defined."></i>
-                        {% endif %}
-                    </a>
-                    )
-                {% endif %}
+    {% if collection.collection_type == "QUE" %}
+        (<a href='{% url "atlas:collection_case_questions" casedetail.collection.pk casedetail.case.pk %}'>
+            {% if casedetail.question_schema %}
+                <i class="bi bi-question-square text-success" title="This case has questions defined."></i>
+            {% else %}
+                <i class="bi bi-question-square text-danger" title="This case has no questions defined."></i>
+            {% endif %}
+        </a>
+        )
+    {% endif %}
 
-                {% if casedetail.case.previous_case %}
-                    (<a href='{% url "atlas:collection_case_priors" casedetail.collection.pk casedetail.case.pk %}'>
-                        <i class="bi bi-link-45deg" title="Manage priors"></i></a>)
-                {% endif %}
+    {% if casedetail.case.previous_case %}
+        (<a href='{% url "atlas:collection_case_priors" casedetail.collection.pk casedetail.case.pk %}'>
+            <i class="bi bi-link-45deg" title="Manage priors"></i></a>)
+    {% endif %}
 {% endpartialdef %}
 
 {% block content %}
@@ -42,6 +42,17 @@
         Collection Type: {{collection.get_collection_type_display}}<br />
         Self review: {{collection.self_review}}<br />
         Open access: {{collection.open_access}}<br />
+        {% if collection.prerequisites.exists %}
+            Prerequisite collections:
+            <ul>
+                {% for prereq in collection.prerequisites.all %}
+                    <li>
+                        <a href="{% url 'atlas:collection_detail' prereq.pk %}">{{ prereq.name }}</a>
+                        &nbsp;
+                    </li>
+                {% endfor %}
+            </ul>
+        {% endif %}
     </div>
 
 
@@ -58,14 +69,17 @@
             <p>Review collection <a href='{% url "atlas:collection_viva" collection.pk %}'>here</a>
     {% endif %}
 
+
+
+
     <h3>Cases</h3>
     <ol id="full-question-list" class="sortable">
         {% for casedetail in casesdetails %}
             <li data-question_pk={{casedetail.case.pk}}>
 
-                
+
                 <a href="{% url 'atlas:collection_case_view' pk=collection.pk case_number=forloop.counter0 %}">Case {{forloop.counter}}</a>
-                : 
+                :
                 {% if casedetail.case.series.count == 0 %}
                     &nbsp;<i class="bi bi-exclamation-circle text-warning" title="No series attached to this case"></i>&nbsp;
                 {% endif %}
@@ -114,6 +128,14 @@
             <div id="user-list"></div>
 
         </details>
+        <p>
+            <button
+                title="Sync users from all prerequisite collections into this collection"
+                hx-post="{% url 'atlas:collection_sync_prerequisite_users' collection.pk %}"
+                hx-swap="outerHTML"
+                class="btn btn-sm btn-secondary"
+            >Sync prerequisite users</button>
+        </p>
     {% endif %}
     {% include 'exam_overview_js.html' %}
 {% endblock %}
diff --git a/atlas/templates/atlas/collection_take_start.html b/atlas/templates/atlas/collection_take_start.html
index c09f4b46..90ca5c4d 100644
--- a/atlas/templates/atlas/collection_take_start.html
+++ b/atlas/templates/atlas/collection_take_start.html
@@ -6,6 +6,7 @@
     {% if request.user.is_authenticated and valid_user %}
         User: {{request.user}}<br/>
 
+
         {% if cid_exam %}
             Started: {{cid_exam.start_time}} <br/>
 
diff --git a/atlas/templates/atlas/prerequisite_required.html b/atlas/templates/atlas/prerequisite_required.html
index cc13e0a9..a03cfc86 100644
--- a/atlas/templates/atlas/prerequisite_required.html
+++ b/atlas/templates/atlas/prerequisite_required.html
@@ -5,7 +5,12 @@
   <p>{{ message }}</p>
   {% if prereq %}
     <p>
-      You must complete the collection: <a href="{% url 'atlas:collection_take_start' prereq.pk %}">{{ prereq.name }}</a>
+      You must complete the collection:
+      {% if cid and passcode %}
+        <a href="{% url 'atlas:collection_take_start' prereq.pk %}?cid={{ cid }}&passcode={{ passcode }}">{{ prereq.name }}</a>
+      {% else %}
+        <a href="{% url 'atlas:collection_take_start' prereq.pk %}">{{ prereq.name }}</a>
+      {% endif %}
     </p>
   {% endif %}
   <p>
diff --git a/atlas/urls.py b/atlas/urls.py
index 13e136cc..e61c4adf 100755
--- a/atlas/urls.py
+++ b/atlas/urls.py
@@ -80,6 +80,11 @@ urlpatterns = [
         views.collection_take_start,
         name="collection_take_start",
     ),
+    path(
+        "collection/<int:pk>/sync_prerequisite_users",
+        views.collection_sync_prerequisite_users,
+        name="collection_sync_prerequisite_users",
+    ),
     path("collection/<int:pk>/authors", views.CaseCollectionAuthorUpdate.as_view(), name="collection_authors"),
     path(
         "collection/<int:pk>/toggle_results_published",
diff --git a/atlas/views.py b/atlas/views.py
index 3f109380..552aba99 100755
--- a/atlas/views.py
+++ b/atlas/views.py
@@ -2189,9 +2189,7 @@ def collection_take_start(request, pk, cid=None, passcode=None):
     Returns:
         _type_: _description_
     """
-    print(f"Collection take start: {pk}, cid: {cid}, passcode: {passcode}")
     collection = get_object_or_404(CaseCollection, pk=pk)
-    print(f"Collection: {collection}")
 
     try:
         collection.check_user_can_take(cid, passcode, request.user)
@@ -2204,7 +2202,7 @@ def collection_take_start(request, pk, cid=None, passcode=None):
         return render(
             request,
             'atlas/prerequisite_required.html',
-            {'message': str(e), 'prereq': prereq},
+            {'message': str(e), 'prereq': prereq, 'cid': cid, 'passcode': passcode},
         )
 
 
@@ -2626,7 +2624,7 @@ def collection_take_overview(
         collection.check_user_can_take(cid, passcode, request.user)
     except PrerequisiteRequired as e:
         prereq = getattr(e, 'prereq', None)
-        return render(request, 'atlas/prerequisite_required.html', {'message': str(e), 'prereq': prereq})
+        return render(request, 'atlas/prerequisite_required.html', {'message': str(e), 'prereq': prereq, 'cid': cid, 'passcode': passcode})
 
     cid_user_exam = collection.get_or_create_cid_user_exam(
         cid=cid, user_user=request.user
@@ -2703,7 +2701,7 @@ def collection_case_view_take_answers(
         collection.check_user_can_take(cid, passcode, request.user)
     except PrerequisiteRequired as e:
         prereq = getattr(e, 'prereq', None)
-        return render(request, 'atlas/prerequisite_required.html', {'message': str(e), 'prereq': prereq})
+        return render(request, 'atlas/prerequisite_required.html', {'message': str(e), 'prereq': prereq, 'cid': cid, 'passcode': passcode})
 
     case, case_count = collection.get_case_by_index(case_number, case_count=True)
 
@@ -2756,7 +2754,7 @@ def collection_case_view_take(
         collection.check_user_can_take(cid, passcode, request.user)
     except PrerequisiteRequired as e:
         prereq = getattr(e, 'prereq', None)
-        return render(request, 'atlas/prerequisite_required.html', {'message': str(e), 'prereq': prereq})
+        return render(request, 'atlas/prerequisite_required.html', {'message': str(e), 'prereq': prereq, 'cid': cid, 'passcode': passcode})
 
     case, case_count = collection.get_case_by_index(case_number, case_count=True)
 
@@ -3563,6 +3561,64 @@ def collection_question_schemas(request, exam_id: int):
     )
 
 
+@user_is_collection_author_or_atlas_editor
+def collection_sync_prerequisite_users(request, pk: int):
+    """Copy valid cid_users and user_users from all prerequisite collections into this collection.
+
+    This endpoint is intended to be called via HTMX from the collection detail page.
+    """
+    if not request.htmx:
+        raise Http404("Invalid request")
+
+    collection = get_object_or_404(CaseCollection, pk=pk)
+
+    # Collect the closure of collections: the target collection and all prerequisites (recursively)
+    to_visit = [collection]
+    visited = {}
+    while to_visit:
+        col = to_visit.pop()
+        if col.pk in visited:
+            continue
+        visited[col.pk] = col
+        for p in col.prerequisites.all():
+            if p.pk not in visited:
+                to_visit.append(p)
+
+    collections = list(visited.values())
+
+    # Compute the union of all cid users and user users across the set
+    union_cid_users = set()
+    union_user_users = set()
+    for col in collections:
+        union_cid_users.update(list(col.valid_cid_users.all()))
+        union_user_users.update(list(col.valid_user_users.all()))
+
+    # Apply the union to each collection and count additions
+    total_added_cid = 0
+    total_added_user = 0
+    per_collection_added = []
+    for col in collections:
+        added_cid = 0
+        added_user = 0
+        for cid_user in union_cid_users:
+            if not col.valid_cid_users.filter(pk=cid_user.pk).exists():
+                col.valid_cid_users.add(cid_user)
+                added_cid += 1
+        for user in union_user_users:
+            if not col.valid_user_users.filter(pk=user.pk).exists():
+                col.valid_user_users.add(user)
+                added_user += 1
+        if added_cid or added_user:
+            col.save()
+        total_added_cid += added_cid
+        total_added_user += added_user
+        per_collection_added.append((col.pk, added_cid, added_user))
+
+    return HttpResponse(
+        f"Two-way sync complete — total added: {total_added_cid} cid(s), {total_added_user} user(s)."
+    )
+
+
 def collection_reset_answers_user_list(request, exam_id: int):
     if request.htmx:
         collection = get_object_or_404(CaseCollection, pk=exam_id)