diff --git a/book/_toc.yml b/book/_toc.yml
index 343f96e..5a86c15 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -69,7 +69,7 @@ parts:
       sections:
       - url: https://classroom.github.com/assignment-invitations/4b010a0969b75b7787a0af82c24a4d4a
         title: "Practice: Effective Low-Dimensional Systems"
-      - url: https://classroom.github.com/a/6Z3Z3Z3_
+      - url: https://classroom.github.com/a/8wy0Ss-1
         title: "Quiz: 2D P-in-Box"
 
     - file: Postulates.ipynb