Revealing mistake: On Billy's first day of school when he is outside waiting for the bus and it just passes him you hear the noise of kids on a bus, but when it passes no one is in it.
Continuity mistake: In the scene when Billy and the bad guy are facing off in the "learning decathalon" and they are doing some science stuff, Billy pulls a shoe out of the boiling pot - it is his right shoe but he has his right shoe on his foot too.
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.
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: After chasing the penguin, his shirt is unbuttoned and he falls. When Juanita pulls him off the ground and tells him to get dressed, his shirt is buttoned.
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: 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.
Revealing mistake: When the car is falling off the cliff you can clearly see that there is 1 person in the car, it's not packed with the whole family like before.
Visible crew/equipment: When Billy shows that he stole the shirt from Frank and lifts it up, you can see the microphone wire on the side of his stomach.
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.
Visible crew/equipment: When the students go to Principal Anderson's house, you can see the shadow of a crew member in a room behind the principal.
Revealing mistake: When Eric gets mad at Max, chucks his stapler, and hits his secretary, the stapler is already on the floor when she gets hit.
Continuity mistake: When Billy puts a suntan lotion smiley on his chest it changes. One time it is running down and then not.
Continuity mistake: During the scene where Billy, Miss Vaughn and the students are doing the singing number, the sky changes from mid-day sun, afternoon sun, to overcast when you see the clown lying on the ground back to late afternoon sun.
Continuity mistake: When Ms.Vaughn goes to beat up Billy and he is sleeping on the ground he has the lobster float on his chest, but in the next shot it is around his neck, and then it isn't.
Continuity mistake: When Billy is in 3rd grade, and Ms.Vaughn is sick and the class is going crazy, the kid dancing on the desk is on the left desk, and when the scene changes back to him he is on the right desk.