Continuity mistake: After Molly Ringwald does her trick, she puts the lipstick away twice. It has a shot of her putting it away from the front and then another one from the back.
Continuity mistake: Various times throughout the movie, Judd Nelson is wearing the diamond ear ring Molly Ringwald gives to him when her parent picks her up from detention at the end. It is very different than the lightening bolt earring, so there's no way to confuse them.
Continuity mistake: After the whistling scene, Bender is holding a pencil. When Andrew is talking you can see Bender in the background playing with the pencil. The camera cuts back and forth between him and Bender throughout the scene. But when the camera zooms in on Bender when he's talking, he has nothing in his hands.
Continuity mistake: When Vernon is in the basement files and Carl walks in, the card in the drawer is tilted and it stays this way for a few shots. In the next shot, the card is straight, but in the shot after that, it is tilted again.
Continuity mistake: When Judd Nelson enters the library, he walks up to Brian's table and motions to him with his hand to move to another table. He uses his left hand, but when the camera-angle changes and shoots Judd Nelson from behind, he is suddenly pointing with his right hand.
Continuity mistake: When Bender takes the screw out of the door, the chair that Vernon tries to use to keep the door open is not there when he walks in. When he goes to use it, however, it is right next to him.
Continuity mistake: The scene where Bender and Vernon are in the closet, Vernon tells John to take a swing at him and points to his chin. Now in the frontal view he is pointing to his chin with his right hand, but from the back view it shows him pointing with his left hand, then it goes back to the front with him pointing with his right.
Continuity mistake: When Bender is escaping through the ceiling, his wallet chain is seen on his left side. That is where it is throughout the whole movie. Except when he's crawling back to the little room through the ceiling, it is seen on his right side.