Sports uniforms worn while playing a sport are irrelevant to dress for the classroom.
At my high school and our kids high school’s a lot of kids wore school football jerseys on game day, again the ones you could buy at the school store.
I went to school in the 60’s and our kids in the 80’s, all at different schools, and every one had a school store where you could buy jersey’s, school shirts, pretty everything labeled with the school ‘logo’ and name.
I never saw that until college, which I began in 1984. You must have lived somewhere that was more advanced in marketing.