Do you think that following fashion is good or bad for students?
In an ideal word, no. That's one reason why we have uniforms, so that no kids may get bullied because of their style of clothing (or whatever their parents were able to afford).
Students should focus completely on their studies and realise that EVERYTHING else that happens in school is NOT important in terms of the rest of their lives.
But that's one of those things you cant teach! You only realise how stupid you were when you were a kid once you grow up and look back at how you spent your time etc.
O well...what can you do?