When I was a teacher and head I did not allow “fun” slippering. If it was done, it had to be done properly. By that I mean placed firmly across the bottom, be it clothed or not.
One suggestion has been made on this site that teachers did these fun slipperings because they enjoyed it. Of course they may be right, that is why fun slippering is wrong. I can tell you that their is nothing pleasurable about a boy bending over in front of you waiting to have a coule of heftfy whacks on his bottom from you. It is even worse if its to be done on the bare flesh and you see the slipprer mark on the bottom after it has been hit.
Theior is , nor should be, any fun for anybody in slippering a boy