not all Head’s supported their class teachers in matters concerning CP so this technique would only work if the Head in question was one who believed that a visit to him by a pupil was not something the pupil would ever want to happen to him again.
There was also a feeling in Scottish educational circles that punishing the buttocks, even when covered with outdoor clothing, was somehow inappropriate, an embarrasment. especially if girls were present, and not part of Scottish education. Punishment on the clothed buttocks was banned back in the late 1950’s after which only the hands could be chastised and then only with a leather strap.
I can only say that the system worked. There was variation in the level of punishment according to the deed and the class teacher was respected, and sometimes feared, as a figure of authority including in matters concerning punishment.