Truancy is a mechanic in Bully.
If Jimmy fails to attend a class that he hasn't yet passed, he is considered truant. Authority figures will be on the lookout for him. If he is busted on campus by a Prefect or Faculty, he'll be taken directly to class. If he's busted by a police officer, he'll be dropped off at the front gates of the school.
Jimmy is the only student that can be truant. Other students gradually despawn during class time, but authority figures leave them alone even if they see them.
Once Jimmy has passed a class, he can skip it without being considered truant.