Why isn't tipp-ex allowed in some schools?

Oh, dude, tipp-ex isn't allowed in some schools because it can be used to cheat on tests by covering up mistakes or changing answers. I mean, it's like having a magical eraser that can erase all your wrong answers and make them disappear into thin air. But hey, schools want you to learn from your mistakes, not cover them up with some sneaky white-out, right?