I think very early in my school days--the early 90s--I was at least assumed to be right handed for no reason other than because everybody is and teachers defaulted to teaching me, and everybody else, with the right hand only. (Even going so far as to teach left from right by saying, 'The RIGHT is the hand you WRITE with!', which obviously didn't work out very well.) I don't really remember being FORCED to do it, just that it was automatically assumed I WOULD be right-handed. There wasn't any major drama when it became clear I was a lefty and nothing was going to change that. I was never in a class my entire school career with more than one other left-handed person and we were always relegated to the back or a corner of the room so we wouldn't hit our elbows on other people.
Not even my parents thought I was going to be left-handed. There's no one--really, NOBODY--from either branch of my family with this trait to have passed it on to me. Only one of my great-grandfathers was a lefty and he was forced to be right-handed in school. When he left school he switched back because nobody was making him do it anymore.