When I was a prefect (about 1966, I suppose) I remember sitting in the prefects room when one of my colleagues arrived, with a third-former who was a well-known rogue and hard nut – he’d even been in front of magistrates, though in fact I discovered that he was susceptible to acts of kindness. Anyway, this lad had been caught smoking and the prefect who brought him asked the head boy what should be done. The response was immediate: “take him to the headmaster”.
Some time later the prefect returned, and of course we all asked him what had happened: “three on the arse” was the response. So I guess he watched the punishment take place.