It really never came up; again, this was 30+ years ago. I can’t think of a single instance where a girl hit a boy. I don’t think she would assume the boy wouldn’t hit her back, since young boys aren’t necessarily gentlemen yet.
Either you are trying to pretend this doesn't happen to excuse fathers from failing to defend their sons against this sexism, or your parents really did manage to find a school system that protected all students equally. If the latter, then good for them.