Continuity mistake: When Billy is in first grade, Miss Lippy sits all the kids down in a circle for story time. One little girl goes up to Billy and says, "You have a mis-shaped head.", while she stands in front of Billy. In the very next shot, you see her stepping over Billy's leg to sit in front of him. (00:18:50)
Continuity mistake: When Billy is on the bus and the kid dares him to touch Ms. Vaughn, when the camera is looking at the back of Billy's head, you can see in the background that Ms. Vaughn is 3 seats in front of him. Then after he tries to grab her and goes back to sit back down his seat is only 2 seats back.
Continuity mistake: When Billy and Veronica are singing when Billy decides to go back to school, Veronica is on the left side. While standing in front of the fountain, they turn to see the kids who are singing, but Billy and Veronica have switched positions. They are standing in the same spot, but since they've turned around, Billy should now be on the left and Veronica on the right.
Continuity mistake: When Billy is chasing the penguin, he chases the penguin from the front yard and goes around to the back yard, but when he falls down attempting to grab the penguin, he appears at the front door and you can see when the limos stop, there's the gate where he ran over the flowers and the maintenance guy threw down the hoe.
Continuity mistake: In the scene where Veronica comes to Billy's house, tosses him in the pool and starts beating him up, watch the people on the side of the pool. First, the chubby guy and Frank are sitting in lounge chairs and you see a third person's legs on one of the chairs. Then the next time they cut to them, the third set of legs is gone, and Frank is lying on the chair where the legs were. When they cut back again, Frank is back in the first chair and there is no third pair of legs.
Continuity mistake: When Billy, Frank, and that other guy throw pickles at the fast-food restaurant window to see which one will slide down the fastest, the pickles' respective positions on the window change significantly from when they're thrown to when the actual "race" is occurring. The position then changes again after the race is over and the pickles are still visible in the background. (00:08:50)
Continuity mistake: In the scene where Billy is getting drunk again, he opens a can of Budweiser, takes a swig, and drops it to the floor. But when it hits the floor it makes the sound of a empty can.
Continuity mistake: In the scene where he has to write in cursive the words change shape as though they wrote it a few times making the scene. It's around the time he is throwing the fit.