Kids should be able to show their true personalities every once in a while. They need to show the world their sense of style and clothing. School uniforms are boring and should only have to be worn on days that you have to. Schools should let their students have more casual clothes days.
I went to a high school that had a dress code. I think the only "code" there should be is something that defines what is too revealing. Otherwise, There should be no code at all.
The problem is that during this period of children's lives, They are trying to express themselves and find out what they like. When you make everyone homogenized, It makes it harder for people to find their place.