Now you need to stick up for yourself. If the admin supports you, then say along the lines that they are distracting you from the other X number of students and are interrupting their instruction. You dont care where they go, they just will not be allowed in the band hall anymore.
If they still do that, bring kids into counselors office and sit them down and tell them that they need changed now, dont care if they sit in office or if they put in a grade for the band class, you just need them out.
Do what YOUR personality calls for. Stick up, but dont do anything here word for word, adapt it to your personality and your relationship with your administration.
Then if it is still not resolved, go to super.
Yep. I came back in but if I get to a point where I want some kids who are destroying the band out, the admin. has a choice. Either the kid goes or I go. And if they would rather keep a behavior problem than me, that's fine. Here's the keys. Bye!