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.
Continuity mistake: At the opening of the film when Billy is in the pool, after he puts the suntan lotion on and realises that it is nudey magazine day, he begins to wade out of the pool. In the side on shot he is holding a wineglass, but a split second later the wineglass has vanished.
Continuity mistake: When Billy and his third grade class are on a field trip to what seems to be a farm, watch the kid next to the tour guide lady with a stripe t-shirt. After about 30 seconds he and another 2 kids come running from the back of Ms. Vaughn and Billy telling them that their lunches have been stolen. How can they have been in 2 places at once? (00:41:21)
Continuity mistake: When Veronica comes to Billy's house, she starts beating the crap out of him, and then pushes him into the pool. During that whole fight, she never even goes underwater, but her hair seems to be wet all over. After she starts getting through to Billy and talking to him, her hair is dry at the top. The only parts that are wet are her tips which are actually in the water. (00:05:50)
Continuity mistake: When Billy and the people who work at the mansion are playing kickball, after he runs to second base, the sign in the background says something about Billy's team always winning. But when the camera cuts to the 2 nurses on first base the sign is in mid-stroke of changing into something entirely different. And the camera change is too quick for it to have done that automatically.
Character mistake: When Billy comes back from high school to visit his 3rd grade class, Ms. Vaughn is teaching prime numbers. The board reads "1, 3, 5, 7, 11" with the words "prime numbers" below it. "1" is not a prime number and it is written on the board, and "2" is a prime number and it is not written on the board.
Continuity mistake: During the singing number where Billy decides to go back to school, Billy, Veronica, the kids, and the clown are on the front lawn. Billy is standing on Veronica's left. However, in a wide shot when they start "Do you have any more gum?" Billy is on Veronica's right.