Theory Comment

So there are 24 kids in the theory class and it started out with only a few kids talking all the time, but now every single kid talks. It doesn't help that they are on different levels of musicianship too. On Friday they were so bad that they wouldn't even quiet down for my co-op. I've moved around their seats but that doesn't do anything because they all talk, not just one person. The other music teachers in the department have observed this to and they all think that the class should have been split into 2 seperate sections, but that's simply not going to happen this year. I get them quiet for 5-7 minutes but then it just starts back up again. They're all good kids and a good handful don't mean to cause trouble, but they don't realize that the talking echoes in that room and how loud it gets. The schedule that I'm on is a rotating block schedule so the class doesn't meet at the same time every day. So, I used to think they were the rowdiest when the class met right after lunch or during last period. I've come to find that they act the same way no matter the time, though. I really don't know what to do and it's getting worse and worse. My co-op is worried about how he is going to teach the class after December because he won't have the extra hand there to help. My co-op and I have devised a system for this class that we split it up (he takes half and I take the other). The talking is just as bad when they are split, though. Any suggestions on how to keep them quiet for more then 5 minutes? I've tried to give them multiple things in order to keep them focused but they still talk.