Some of the slipperings described here do seem rather severe,, At grammar school it was pretty rare for 2 smacks to be exceeded, though one boy did get six. I didn’t witness this but was told the smacks were not too severe.
Just two smacks could seriously hurt, particularly in PE wearing just tight shiny shorts which I suspect the teacher enjoyed the sight of. It was certainly very entertaining to watch other boys get it. I was quite shocked the first time I was slippered at grammar school as I hadn’t expected it to hurt that much. It was only two smacks as well.
I did get two token slipperings at junior school from a female teacher but these were very soft smacks. What hurt more was a spanking from a male teacher who lined up about six of us and gave us each quite a hard spanking, probably about ten smacks. It was nothing like the pain of the slipper though.