When I was in school in the 90s (and the 80s, for that matter), we had physical education classes. We ran around the playground, or the gym, we probably played tennis and basketball and many other things I wasn’t any good at because my coordination is poor and they didn’t interest me. I don’t remember having uniforms, though it’s completely possible we did. It is highly unlikely, however, that they were anywhere near as cute as this 1950s gym uniform I found on ebay:
The label indicates that it’s “Sanforized,” a common term in the mid-20th century for what we now might call “pre-shrunk.” Developed in the 1920s by Sanford Lockwood Cluett, the process involves moistening, stretching, heating, and expanding until the fabric shrinks uniformly and can be made into garments (or whatever) that won’t shrink a great deal when washed.