diff --git a/packages/scratch-gui/src/components/classroom-modal/shared-assignment-catalog.jsx b/packages/scratch-gui/src/components/classroom-modal/shared-assignment-catalog.jsx
index c7308af6de..edc94587b0 100644
--- a/packages/scratch-gui/src/components/classroom-modal/shared-assignment-catalog.jsx
+++ b/packages/scratch-gui/src/components/classroom-modal/shared-assignment-catalog.jsx
@@ -438,8 +438,8 @@ const SharedAssignmentCatalog = ({ group, isLoading, shared }) => {
                 </h3>
                 <button data-testid="shared-catalog-close" type="button" onClick={shared.handleCloseCatalog}>
                     <FormattedMessage
-                        defaultMessage="Cancel"
-                        description="Cancel button that leaves the shared catalog"
+                        defaultMessage="Back"
+                        description="Go back from the shared catalog to the assignment list"
                         id="gui.classroom.shared.catalogClose"
                     />
                 </button>
diff --git a/packages/scratch-gui/src/locales/en.js b/packages/scratch-gui/src/locales/en.js
index a72769defa..9a65eee272 100644
--- a/packages/scratch-gui/src/locales/en.js
+++ b/packages/scratch-gui/src/locales/en.js
@@ -373,7 +373,7 @@ export default {
     'gui.classroom.shared.published': 'Published to みんなの課題: "{title}" (© {author} / CC BY 4.0)',
     'gui.classroom.shared.openCatalog': 'Find in みんなの課題',
     'gui.classroom.shared.catalogTitle': 'みんなの課題 — assignments shared by teachers nationwide',
-    'gui.classroom.shared.catalogClose': 'Close',
+    'gui.classroom.shared.catalogClose': 'Back',
     'gui.classroom.shared.tabAll': 'Browse all',
     'gui.classroom.shared.tabMine': 'My posts',
     'gui.classroom.shared.filterAllLevels': 'All school levels',
diff --git a/packages/scratch-gui/src/locales/ja-Hira.js b/packages/scratch-gui/src/locales/ja-Hira.js
index 0f00609dda..942c8d5fc9 100644
--- a/packages/scratch-gui/src/locales/ja-Hira.js
+++ b/packages/scratch-gui/src/locales/ja-Hira.js
@@ -431,7 +431,7 @@ export default {
     'gui.classroom.shared.passcodeImportBtn': 'このクラスにとりこむ',
     'gui.classroom.shared.openCatalog': 'みんなのかだいからさがす',
     'gui.classroom.shared.catalogTitle': 'みんなのかだい — ぜんこくのせんせいがきょうゆうしたかだい',
-    'gui.classroom.shared.catalogClose': 'キャンセル',
+    'gui.classroom.shared.catalogClose': 'もどる',
     'gui.classroom.shared.tabAll': 'すべて',
     'gui.classroom.shared.tabMine': 'じぶんのとうこう',
     'gui.classroom.shared.filterAllLevels': 'すべてのがっこうしゅ',
diff --git a/packages/scratch-gui/src/locales/ja.js b/packages/scratch-gui/src/locales/ja.js
index a018aff8d6..7698d067ac 100644
--- a/packages/scratch-gui/src/locales/ja.js
+++ b/packages/scratch-gui/src/locales/ja.js
@@ -422,7 +422,7 @@ export default {
     'gui.classroom.shared.passcodeImportBtn': 'このクラスに取り込む',
     'gui.classroom.shared.openCatalog': 'みんなの課題からさがす',
     'gui.classroom.shared.catalogTitle': 'みんなの課題 — 全国の先生が共有した課題',
-    'gui.classroom.shared.catalogClose': 'キャンセル',
+    'gui.classroom.shared.catalogClose': '戻る',
     'gui.classroom.shared.tabAll': 'すべて',
     'gui.classroom.shared.tabMine': '自分の投稿',
     'gui.classroom.shared.filterAllLevels': 'すべての学校種',
diff --git a/packages/scratch-gui/test/unit/components/shared-assignment-catalog.test.jsx b/packages/scratch-gui/test/unit/components/shared-assignment-catalog.test.jsx
index 7c4fbaaf80..26ea45e1c4 100644
--- a/packages/scratch-gui/test/unit/components/shared-assignment-catalog.test.jsx
+++ b/packages/scratch-gui/test/unit/components/shared-assignment-catalog.test.jsx
@@ -163,6 +163,19 @@ describe('SharedAssignmentCatalog (issue #1070)', () => {
         expect(shared.handleLoadMoreCatalog).toHaveBeenCalled();
     });
 
+    test('the header back button is labelled "Back" and returns to the assignment list (issue #1121)', () => {
+        const shared = sharedState();
+        renderCatalog(shared);
+        const back = byTestId('shared-catalog-close');
+        expect(back).toBeInTheDocument();
+        // Label must read "戻る" (Back), not "キャンセル"/"閉じる".
+        expect(back.textContent).toBe('Back');
+        // Clicking it only closes the catalog, returning to the assignment
+        // board (課題一覧) — it must not navigate to the class list.
+        fireEvent.click(back);
+        expect(shared.handleCloseCatalog).toHaveBeenCalled();
+    });
+
     test('the mine tab hides the filters and marks unlisted items', () => {
         renderCatalog(sharedState({
             catalogTab: 'mine',