You have certainly confirmed the established folklore concerning the gym mistress, ensuring that the many cynics and doubting Thomases out there will be dining on a meal of humble pie for quite some time.
It seems that there was indeed more corporal punishment of girls at your school than you were possibly aware of at the time. However that confirms my argument that in a mixed school girls would always be seen to privately with only the other girls present.
Also the head mistress seemed a tad severe. I think it would have been wise for most girls to have given her a very wide berth at the time.
