Do Public Schools Actually Have a Uniform?

Young Adult Girls wearing similar outfits after school.

Recently in American Studies, we had a conversation about if public schools actually have a "uniform".  Our teacher noticed a few years back, there was an overwhelming majority of kids who wore North Face Jackets to school. Then an even bigger anomaly occurred. I can safely say 95% of girls at our school started wearing Ugg Boots. Why is it that we don't have to dread putting on "the plaid skirt high socks" private school uniform, when we all wear very similar things anyway. The Guardian reports that "the thought of school uniforms makes some people cringe", yet why are public school students wearing similar clothing?

Why do you think kids tend to dress similar to their peers?