In the toilets scene, Lolita exits the lavatory and closes the door twice in two different shots.
While in the gymnasium listening to a speech, there are three bullies sitting behind Dawn spitting spit balls at her. She is spit ball-free in one shot, but in the next shot, a close-up, she has several on her.
When Dawn is talking to Brandon in the clubhouse, she is leaning over so her bra (or perhaps a white undershirt) is showing through her sweater. In the exact same shot a few seconds later, it's covered up, even though she hasn't moved.
It's never explained or shown why the principal or a teacher or any other staff member won't do anything about the bullying. A teacher was sitting next to Brandon and his friends during an assembly while they were shooting spitballs and the teacher didn't tell them to stop. Brandon and his friends could've gotten expelled for bullying Dawn and punching another boy and Lolita could also get expelled for refusing to let Dawn leave the girl's bathroom unless she poops. The principal could also get fired for negligence.
When Steve is Singing "Welcome to the Dollhouse", his lip movements do not match up with the words when the scene is up close of him about to finish the song. this is due to another actor dubbing his singing voice.
In the scene where Mrs Grissom accuses Dawn and Brandon of cheating, she says "Brendan" instead of Brandon.
In the principal's PA address he says, "Good morning, students..." but the clock next to the speaker shows the time as 12:30.