I was in school just as they were moving away from mandatory showers after gym class. In junior high, we were required to shower. At the end of class, we all went back to the locker room. We had to undress and put our clothes in our lockers, then proceed naked to the shower area. We had about 5 minutes to shower and the teachers monitored us to make sure that everyone was showering.
Showers weren't required by the time I got to high school. Most of the guys in my grade were used to them, so we took showers anyway. The younger classes that came after us didn't like to shower. Grades were mixed together in gym, so there were a mix of guys walking around naked and guys that never took off their underwear or changed under towels.
Showering with my classmates was embarrassing at first, but it did get me more comfortable with my body. Because we were all in the same situation, no one ever made fun of anyone else for getting hard, which happened to pretty much everyone at least once.
From what they tell me, none of the students shower at my kids' school. I've encouraged my son to shower when we go to the gym, and he's reached the point where he doesn't mind walking around naked there.