In middle school the locker room had showers but we were not allowed to use them after gym class. I vaguely remember being told they were for the sports teams, but I wasn't on those so who knows if they were ever used. In my high school, which was renovated about 1996, the locker room had one, private shower, so forget about making it mandatory. Its use, however, was permitted and it was not uncommon for one or two people to quickly rinse off after class.
I'm sure all the teachers would prefer kids to shower, but clearly school policy in my area has changed to prevent kids from showering communally. I assume this has something to do with the rise of political correctness and the litigious nature of American culture. Also, smelly kids are a small price to pay in an age where most kids have camera phones and unfettered internet access. Forty years ago little Ricky might have been teased or even tormented, but today it could easily result in the propagation of CP.