I would say most of the extensive use the PE masters put the slipper too certainly to let the lad feel it but was often a warning to sort themselves out and a warning that if they or anyone continued to mess up a fuller “of the best” slippering would be given out and they certainly didn’t worry about given out real hiding when they deemed it deserved – my only real gripe would be that PE teachers were more often into group punishment and didn’t worry about finding the wrongdoer – if there was a group of lads together a disturbance they often the whole group found themselves doing press up, gym laps or even at times each getting a quick few strokes of the slipper.