Remembering a movie

This is kind of vauge but like 5 years ago I saw previews for a movie, but I never saw it and I don't remember what the title is but I want to see it. It was about these kid who started controling their school, by like showing the student body the bullshit that they were being put throught. Like taking control of assemblies, and putting up posters and stuff. If you have any idea what this might be give a shout.