I am in the same situation as you. My Ancient History class is incredibly disruptive, and our teacher, as good as he may be, only came this year and cannot control the class.
I have the same teacher for my Legal Studies class, however Legal Studies is different, all the committed students who want to do well sit on one half of the class, while the other half clumps together on the other side. With a setting like this it is easier for me to just block noise out and work with the other students who actually wish to be there.
I find that it's always fun to remind these kids that they don't have to be there, and that if they don't want to learn, they need to either shut up or sign out. If there are other students such as yourself, you can get them to back you up.