Anything that won’t hurt the kids would be a good option. Maybe just put a sign up saying “please do not climb wall – notify your teacher about lost property” and discuss with the teachers.
You could:
-install a lockable fence/door and give the teachers a key.
-Plant some hedges that will grow tall and a few feet wide. This will also stop noise.
-Install a wooden or metal fence on your wall to make it higher.