On an individual level, people mostly just follow the rules on their own. The spectre of some large and unknowable punishment is usually enough to enforce something like this. If 25% of people break the rule because they aren't afraid... You don't have to find all of them and punish them. You can just find a couple and punish them harshly, occasionally, decreasing the number of people who aren't afraid of rhe consequences.

Aside from that, this is implicitly a statement that school admins and teachers aren't allowed to push LLM usage on students. That's FAR more enforceable.