In my area, and I stress my area, hand spanking was not regarded as a punishment to be used at school. It was not effective. Later it was regarded as effective a junior age, but as we moved towards1980, as hand spanking was either bare or over pants parents were starting to question the sexual reasons behind such punishment. I can honestly say, I never recall smacking a child at school over my knee. I have many times put my grandsons over my knees and given their bottoms a smacking.
At school, my hand did land at times on a bottom, if boys were playing about in the changing room. For this it was “Stop Playing about and get changed” backed with a sharp slap on the bottom while the boy was standing up. I do not regard this as the same thing as over the knee.