Audio problem: After throwing what looks like a toilet through the window, the two guys give each other a high-five. Their hands almost completely miss each other, yet we still hear a loud clap.
Audio problem: In the scene when Joe Clark takes Thomas Sams and the other boys into the music room, he slams Thomas Sams into the piano and you hear what sounds to be like keys being pressed down. However, he hit the side of the piano, so the only way sound could have come out is if his hands were over the keys. The way he hit the piano, it was not possible to produce any type of sound.
Chosen answer: They are discussing some of the things that Mr. Clark has done that has "embarassed" the school. They are debating what to do about him. And by "posturing," they mean his insistance on wearing African dress and espousing his political beliefs.