Continuity mistake: When Terry Corrigan goes mad and teaches his students at gun point, he asks one of the thugs a question and holds his gun right up to his face. The tip of the gun is almost touching the thug's face, but from a different angle, the gun is further away.
Revealing mistake: At the end when Mr Norris starts to run through the hallways looking for the punks, he is ambushed and beaten up. If you look closely at his shirt, you can see a small pad underneath on his left, the exact spot where they keep punching him.
Continuity mistake: When Jimmy is at the top of the flagpole, just before he falls off, every time the camera shows his face he is holding the flag straight out with his left arm. Anytime the camera is behind him, the flag is hanging down and both of his arms are wrapped around the flagpole. (00:33:13 - 00:34:00)
Continuity mistake: When the gang catches Artie and his female friend in the alley, the female gang member breaks a bottle on the car. The whole bottle shatters. She then somehow has half a broken bottle in her hand to use as a weapon. (00:37:00)