I believe immediate correction for stepping out of line may have had a useful part to play here. And as Voltaire might have put it, the dramatic effect served “to encourage the others”.
I don’t have a problem with immediate correction . Rather what I was getting at was Christopher’s comment that :
But five of us obeyed the rules and stayed in the changing room. When the teacher arrived he was not pleased!.
He called the class to order and sentenced them to line up for 2 of the slipper (through pe shorts) Then he called us out of the changing room and told us to join the end of the line, ….
and later