The P.E teacher did “like” to slipper boys of the 12 year old age group or so it seemed then, most of the times he would crack the slipper down as in real punishment for last one in the gym or who he said was last in the gym or last one to get changed at the end of the lesson, though at times he would have “fun” slipper-rings as crack the slipper down and stop it just before it hit and give a light tap.
But he did go in for “mass” slipper-rings a number of times in the gym guilty or innocent we all had to touch our toes in turn in a line up. One thing he would often do is get the boys to take off his own plimsol to be slippered with it, Though the boys would try not to do so at times we all did cry at times, Also we noticed at times the slipper got harder as he went down the line, or so it seemed
What I have wrote above does seem to have happened lots of times in schools