--- a/ucs-school-lib/python/models/user.py	
+++ a/ucs-school-lib/python/models/user.py	
@@ -398,7 +398,7 @@ class User(UCSSchoolHelperAbstractClass):
 			return False
 		try:
 			(self.schools or [school]).remove(school)
-		except IndexError:
+		except (ValueError, IndexError):
 			logger.warning('User is not part of school %r. Not removing.', school)
 			return False
 		if not self.schools: