In Brit schools, most commonly the rule was smoking. Why. Cos it gave the perverts and sadists full licence to thrash their targets with little risk of blow-back. When SCP was coming to a close in state schools, one case challenging the practice was that of a girl, leaving the school after her final exam, called back into the headmaster’s office for a “leaving present”. A very standard high kink act of abuse that the pages of our special magazines frequently had as story event.
What many forget or never knew is that smoking by older kids was actually normalised in many schools in the 60s, with kids smoking side by side with the teachers. Then the anti-smoking lobby got this policy reversed, so the kids could be beaten again.