This happened around late 1950 around 1958 or 59 in Wisconsin
It was a small rural school so they had only one class room of each grade, like 7th grade had 32 students, half of them girls and 8th grade had 34 students with 20 of them girls so they all knew each other, and not the girls knew a whole lot more about the males and most did not even try to cover up, we just let it all hang out. For weeks afterward, the girls all talked about how they saw the boys naked. They often said it was nice seeing so much of us as they usually looked at our groin I guess to see if we had an erection which often did when they were reminding us that they saw us naked for several moments and reminded us that we would never see them because males were not allowed in the girls locker room so there would be no accidents like with us. Some of the older boys were invited to a girls house that had a swimming pool and they went skinny dipping while the girls wore their swim suits and the girls had some of the girls from 5th and 6th grade there at those times. I went to one of those parties once or twice and it felt good that even more girls could see me for a longer time without a stich on while they word swim suits. It was under careful supervision by several moms with strict rules that the boys could not touch the girls but they said nothing about the girls not touching the boys and that they did Remember some of us were in 11th and 12th grade so we had adult male genitalia . So much the better for the girls right?
We knew the teachers too and a few years after graduation, one teacher did admit that she and the other teachers set it all up. I told her good job and asked if they ever did it again after that time,=. I also asked if she would ever do that with the girls.
She said that they did do it one other time almost just like the one we are talking about here and that it wild not be possible to do it with the girls for one, the boys would never be allowed in the girls locker room and also she said they would never exposed the girls to males.
I told her that it was was good they did it a second time and that they would never do it to girls because I think males should be naked in a lot of events while girls stay modesty dressed.