When the bully Fang falls off the waterfall he is holding a piece of a broken branch in his left hand. In the next shot the branch in his right hand.
Kirby puts drops in his ear during class. There are four shots of him at his desk. In one of them, the bright green pen is missing from his desk.
When David climbs the rope in the gym to hide from Fang he is at the top of the rope but when Fang finds him he climbs higher by several feet after Fang sets the rope on fire.
Mr Leary spills a drink over his shirt and a bunch of kids are watching him. The shirt collar of one of them changes from sticking out to tucked in.
When the bully is beating up the kid in the playground, the smaller kid is wearing obvious body padding.
When the woman (referred to as Helen) slips on the oil put on the floor by Roscoe "Fang" Bigger, you can see the tail bone pad in her pants to cushion her fall.
Green stage lights are frequently reflected in David's glasses.