Other mistake: When the kids are playing "Carry On Wayward Son," there are no notes on the TV in the one area. However the boys play the notes there and get it right.
Take Me out of the Ball Game - S3-E24
Other mistake: When Peggy strikes Bill in the head in the softball game, he gets hit on the left side of his head. Later in the scene he is using an ice bag on his head but he's icing the other side.
The New Kid - S1-E2
Other mistake: At the start when the gang change the time on the clock in the classroom, it wouldn't control the main school clock, plus in every other episode the clock has been operated by The Box on the side of the school, as shown in " The spy who came into the playground".
Opera House Murder Case: File 2 - S1-E22
Other mistake: At the beginning of the episode, the characters are gathered thinking back about part 1 of the case. Amazingly enough, the propmaster's armpit ate the A of his shirt. Now he's not a "BADMAN", he's a "BADMN." (00:02:05)
Other mistake: In one scene in this episode, the clock on the kitchen wall (behind Jake) does not have any hands.