Peterborough has always been a highly disciplined school. There is little else of interest on FR. There are a few comments on discipline found in the school booklet most of the unofficial kind, which when time I will post further.
Punishment books/logs for Peterborough are held at the Archives center and cover a range from 1938-2002 it may well record this incident, I have tried to follow the record reference without much success, but never one to give up.
As you note, even if only the boys were caned that’s 280 odd canings! Assuming, as seems likely in a Primary School, that only the Headmaster used the cane how on earth would such an exercise be conducted? Even at a caning rate of a pupil per minute, that’s nearly 5 hours of solid caning, almost a complete school day allowing for breaks.