diff --git a/copienator/commands/annotating_by_label.py b/copienator/commands/annotating_by_label.py
index 3e252f0..45e769a 100644
--- a/copienator/commands/annotating_by_label.py
+++ b/copienator/commands/annotating_by_label.py
@@ -275,15 +275,7 @@ def _existing_group_state(
 
 def split_batches(rendered):
     batches = []
-    current = []
-    current_height = 0
-
-    def flush() -> None:
-        nonlocal current, current_height
-        if current:
-            batches.append(current)
-            current = []
-            current_height = 0
+    heights = []
 
     index = 0
     while index < len(rendered):
@@ -302,15 +294,17 @@ def split_batches(rendered):
                 f"maximum group height is {MAX_HEIGHT_PX} px."
             )
 
-        # Consider the student's complete block before adding its first image.
-        # Otherwise later images from that same student could overflow the batch.
-        if current and current_height + student_height > MAX_HEIGHT_PX:
-            flush()
-        current.extend(student_items)
-        current_height += student_height
+        # Reuse space in earlier groups, keeping each student's block intact.
+        for batch_index, height in enumerate(heights):
+            if height + student_height <= MAX_HEIGHT_PX:
+                batches[batch_index].extend(student_items)
+                heights[batch_index] += student_height
+                break
+        else:
+            batches.append(list(student_items))
+            heights.append(student_height)
         index = end
 
-    flush()
     return batches
 
 
diff --git a/tests/test_gui_core.py b/tests/test_gui_core.py
index 5e4cdd5..af71f73 100644
--- a/tests/test_gui_core.py
+++ b/tests/test_gui_core.py
@@ -2236,6 +2236,23 @@ class StandardCliTests(unittest.TestCase):
         self.assertIn("Copie01", str(raised.exception))
         self.assertIn("cannot be split", str(raised.exception))
 
+    def test_grouped_batching_reuses_space_in_earlier_groups(self) -> None:
+        module = self.modules["annotating_by_label"]
+        rendered = [
+            ("01", "Ex 1", Image.new("RGB", (10, 70)), 0, []),
+            ("02", "Ex 1", Image.new("RGB", (10, 60)), 0, []),
+            ("03", "Ex 1", Image.new("RGB", (10, 40)), 0, []),
+            ("04", "Ex 1", Image.new("RGB", (10, 15)), 0, []),
+            ("04", "Ex 2", Image.new("RGB", (10, 15)), 0, []),
+        ]
+        with patch.object(module, "MAX_HEIGHT_PX", 100):
+            batches = module.split_batches(rendered)
+        self.assertEqual([[item[0] for item in batch] for batch in batches],
+                         [["01", "04", "04"], ["02", "03"]])
+        self.assertEqual([sum(item[2].height for item in batch) for batch in batches],
+                         [100, 100])
+        self.assertEqual(batches[0][-2:], rendered[-2:])
+
     def test_grouped_annotation_height_limit_is_32000_pixels(self) -> None:
         module = self.modules["annotating_by_label"]
         self.assertEqual(module.MAX_HEIGHT_PX, 32000)