Schools, historically, have been home to discretionary justice. You let the principal or the teacher decide what to do about cheating because you know that every case of cheating is different--and, more to the point, that every cheater is different. Jimmy is incorrigible, and needs the shock of expulsion. But Bobby just needs a talking to, because he’s a decent kid, and Mary and Jane cheated because the teacher foolishly stepped out of the classroom in the middle of the test, and the temptation was simply too much.
What about the student that gives the teacher a poisoned apple? Here.