I'm not making a judgment on kids' behavior there, or saying anybody's no good. I'm talking about odor, pure and simple. Is there a body odor problem in the house?
There was a time, when my daughter was in elementary school, when the issue was, well, right under our noses. Due to a late start in school and a difficult switch from self-contained, she was mainstreamed in a class with kids two years younger. Her emotional development and learning abilities were delayed enough to make that placement perfect, but her physical development, alas, wasn't lagging behind.
Her body was going through changes that her classmates' bodies weren't, and that included the production of major underarm odor. With deodorant not a big issue for her peers, and not a big issue for her immature mindset, it was hard to convince her that, yes indeed, we were not making this up, she needed to wash and anoint her pits.
She swore that nobody but us, her pesky parents, had ever mentioned a problem to her. What she didn't know is that her teachers and aides were complaining to us instead. We finally told everyone who mentioned it to mention it to her, nicely, of course, and I think once she heard it from a teacher she respected, the lightbulb went on.
If you've got a teen with an incomplete appreciation of the need for personal hygiene, consult my list of Body Odor Basics for some tips on tricking that stinker into smelling sweet. Eventually, you hope your young person will start to actually care about this stuff (and indeed, my girl's now odor-obsessed); until then, you'll have to care for the both of you.