Continuity mistake: In the scene were Lloyd finds Harry's "treasure chest", you can see that the chest is laying flat against the wall, but when the Principal and the lunch lady come and find it missing, there is a small dirt outline, as if the chest was pointing out from the wall, instead of larger outline, as if it were flat against the wall.
Continuity mistake: When Ms. Heller is talking to the tour guide at the museum, she offers her a $5 bill to take the tour twice. How the bill is folded changes. When it is a close-up of Ms. Heller the bill is half folded but when the tour guide is pushing away the bill it is fully folded, then it keeps switching back between folds.
Continuity mistake: When Jessica and the principal are in his car watch the driver's side mirror. When Lloyd and Harry are following them you see a side view of the car and it has a regular teardrop mirror. After Lloyd and Harry get ice cream the principal is telling Jessica no one will be looking for her and the side view mirror has gone to a big square truck mirror like welded to the door.
Continuity mistake: When the teacher asks her "special needs class" if they have any ideas for a float, the camera switches between people and conversations and every single time this happens the Chinese exchange student changes position (resting on her elbow, arms out stretched, hands together etc...)