The sock in Cody's shirt during the contest disappears between shots.
Zack puts Cody's whistle in their friend's pudding, but when Cody says "You got pudding on my whistle," the whistle has disappeared.
When Zack and Cody land on the stage before they perform, all of the drums and mikes are pushed over to one side of the stage. In the next shot however, they are all in their normal spots.
When Arwin, Zack, and Cody are talking, the door behind them is opened. But in the shot where they are leaving with the jet propelled skates, the door is closed.
When the Carey is talking to the band and telling them they need a new place to practice, the door is ajar behind her, then it is closed, then ajar again.
The closet door's lock is on backward. It locks from the outside using a "twist lock" but requires a key from the inside. This provides no protection for the contents, but potentially locks people inside.
When Zack and Cody flies out from the laundry cart Cody had a sock on his shirt, but when he starts playing the organ the sock disappears.
During the boys song "School's Out," the singing and playing of instruments is clearly often out of sync.
In the beginning, you can see studio lights reflected on Zack's guitar during the song "Schools Out".
When Arwin comes in with his Saxoblower, he puts on sunglasses and you can easily see studio lights reflected in them.
The reflection of studio lights are visible on the drums almost every time they are seen during this episode.
When Cody tells his mother how much he hated Zack, you can see the reflection of a studio light on the chair he is sitting on.