Continuity mistake: When the boys are watching the girl use the loo, it shows a shot of the ceiling in Janey's classroom (just before the vent falls) and the ceiling is smooth, but when they fall you can see a part of the ceiling has been replaced by some loosely placed white bricks, which would fall easily. When they're on the floor with the turd all over them there are no bricks in sight.
Continuity mistake: The stupid fat guy's supposed to die because he had so many concussions, but in the scene after the football game when he's on a stretcher and it collapses in the background you see him putting his hands out to make sure he doesn't get hurt during the fall.
Continuity mistake: When Catherine is taking off Janie's glasses she leans right in, but when the camera angle changes it shows this to be a larger gap. when the camera flicks around again she appears to be leaning in again.
Continuity mistake: In the scene where Jake walks into the cafeteria and Austin makes fun of him ("he has a thing for butt ugly girls") there are a stack of wrapped sandwiches on sliced bread in front of the fat guy. A moment later, they are unwrapped sandwiches on hoagie buns. (00:49:20)
Continuity mistake: When Mitch is giving the the letter to Amanda, take a look at her hairs: it switch places between scene. (01:29:01)