Honestly,
I think, in the eyes of adults, "middle school students" should not be so-called non-mainstream. .
Too ostentatious is not good,
Personally, I suggest British style.
Basically, it won't be out of date, and both boys and girls are very handsome.
It would be nice to have these points: white shirt (clean and simple style), small vest, black thin tie and plaid. .
Well, my personal opinion is for reference only. I hope I can help you.