My schooling was back in the 1960s- early 1970s and showering was compulsory after PE. (We didn't have deodorants then !)
Showers and changing room were communal, no cubicles or lockers; we just hung clothes on hooks and benches.
The same at the public swimming baths.
It was all matter of fact and noone minded, so teachers just trusted us to get clean.
Anyone who had her period was excused PE altogether that day (no PE without showering), so no worries there.
I've wondered, reading several Mumsnet threads about communal nudity, if social attitudes about this have changed over the last 40 years ? Not just wrt kids, but some adults in gyms, too.
Anyway, this was useful practice for later, when I worked in Germany & Sweden, where I went out with groups of colleagues to communal mixed (naked) saunas and showers.
My current gym has communal showers and changing rooms too, even now. No complaints I know of.