One debate like idea I tried while student teaching 7th graders was to make up a dress code policy. The policy states that there should be certain restrictions on dress, no profanity, no violence, nothing sexually explicit.... etc or use your school's policy. I called my mock school district Valley School District policy and we set it up as a mock situation. The students read the policy, and then were put into one of six groups. Three groups favored the policy and wanted it put into action, and they were as follows: Parent Teacher Organization, School Administrators and Fellowship of Christian Athletes. Three groups were against the policy, they were: Students for Free Speech, ACLU and Vendors, retailers, manufacturers (of the offensive clothing). We spent a good week preparing. Students had to state their position (opinion) and back it up with facts (I said at least 3 facts). Each group got 5-7 minutes to present their view.
They could make signs, posters, etc for extra credit. One thing I would change is that I would invite parents and anyone else who might want to into class and have them vote, acting as a school board. The kids really liked it and it was a great intro into my persuasive writing unit. This really got a heated discussion going, so be prepared!