Continuity: The glass Billy is holding when on his raft disappears. In a deleted scene it shows Billy throwing his glass into the pool.
Continuity: The suntan lotion at the beginning is runny in some scenes but not in others.
Continuity: The position of the "You got a misshaped head" girl changes.
Continuity: The eyes in Billy's grade chart reappear after being poked out.
Continuity: When the third grade was on the bus going to their field trip, the cars behind the bus disappear, and then reappear. Then the bus driver throws out his banana peel, and there are no cars in sight.
Incorrectly regarded as goofs: When Billy is dialing the phone to call the guy he picked on in high school, you hear a phone ringing. This is part of the song being played.
Continuity: During the academic decathlon, when Billy pulls his shoe out of the liquid nitrogen after freezing it, it is a right shoe but he is still wearing his right shoe.
Audio/visual unsynchronized: When Billy is standing at the bus stop, you can hear the sounds of children on the bus that passes, but there are clearly no passengers on the bus.
Continuity: The smiley face on Billy's chest disappears when he approaches the penguin.
Continuity: The suntan lotion smiley face on Billy's chest at the beginning of the film changes drastically between shots.
Continuity: When Eric gets angry that Max revealed his secret about being a wrestler, he throws his stapler at his secretary but when the noise of her getting hit goes off the stapler is already on the ground.
Continuity: When Billy and his friend throw pickles onto the restaurant wall, the positions of the pickles change between shots.
Continuity: When Billy chases the penguin his shirt is alternately buttoned and unbuttoned between shots.
Audio/visual unsynchronized: When Billy's Trans Am pulls up to the high school, we hear the engine being switched off. But the "shaker" in the hood is still shaking, meaning that the car is still running.
Continuity: The snowman that Billy makes in the first grade is clearly not the same snowman that Ms. Lippy gives to Billy before he gets on the bus after school.
Continuity: At the end of the movie, Carl and Billy's dad shake hands. The next shot is Billy talking, and Carl and Billy's dad are in the background shaking hands again.
Errors made by characters (possibly deliberate errors by the filmmakers): Veronica lists the prime numbers in third grade when Billy visits the classroom. This list is missing the number 2, which is a prime number, and includes 1, which is not.
Continuity: In the bus on the way to Billy's third grade field trip, there are three children between Billy's and Ms. Vaughn's seats when we see them from the back of the bus. When Billy is talking with Ms. Vaughn and we are looking toward the back of the bus, there are only two children between Billy's seat and Ms. Vaughn's.
Incorrectly regarded as goofs: When the kids come to Max's house, a shadow can be seen passing behind him in the hallway. This is from a deleted scene when one of the kids dresses up in Max's old wrestling costume and runs out on the lawn.
Continuity: When Billy and his friends throw the pickles on the window for the race, the one on the far right (Billy's) has the lead. In the shot after Billy proclaims himself the winner, the pickle in the middle has the lead.
Continuity: In the academic decathlon, when Billy chooses "Business Ethics" for Eric, the square showing this option is on the left of the game board. When Eric's question is being read and Eric and Billy are shown from the front the "Business Ethics" square is shown at the bottom and in the center of the game board.
Revealing mistakes: When the O'Doyle family station wagon skids off of the road toward the edge of the cliff, the driver is clearly turning the steering wheel in the direction of the cliff.
Revealing mistakes: When the O'Doyle family station wagon skids off of the road. You can see a bracket and a cable on the front end of the car.
Continuity: When Billy goes to see Veronica while drunk, she is wearing a wedding ring in some shots.
Continuity: When Billy writes Rizzuto on the board, the writing style changes slightly between shots.
Miscellaneous: When Billy and Eric are in the academic decathlon, at the last event Eric pulls out the gun and pushes the mike over on the stage. In the next scene you don't see the mike anywhere on the stage.
Anachronisms: When Erik is confronting Principal Anderson and says this is an issue from 1983, as he flips through the pages throughout the scene, you can clearly see a picture of Bret 'The Hitman' Heart in the bottom right hand corner in the magazine. Bret Hart came into mainstream wrestling much later than 1983.
Continuity: When they are on the bus for the field trip, the shots inside the bus clearly show that it is a short bus, while the shots of it on the road show the bus as full size.
Audio/visual unsynchronized: When Jack is spraying a boy with a hose at one of Billy's "graduation" parties, you can hear the boy talking but his lips aren't moving.