Corrected entry: Towards the end, when the band goes to play their second song on stage, it is made clear that everyone (the band and the crew) is on the stage. If that's so, then who's doing the lighting effects?
Corrected entry: As anyone who's ever played in a rock band would know, a room cannot be "sound-proofed" by taping padding around the edges of a door. The noise, especially the drums, would still be heard outside.
Correction: The Principal comes into the classroom in one scene to say that another teacher has reported hearing music, so it seems the soundproofing isn't 100% effective.
Corrected entry: How do the kids know where Dewey lives? I'm sure he doesn't mention it when he's teaching.
Correction: There were all those posters Dewey was posting about wanting to form a band, complete with phone number and such.
Corrected entry: As Dewey is taking a pee in one of the school urinals, you can hear his urine hitting the toilet, but you can't actually see any coming out of him.
Correction: He is standing at an angle to the camera and is blocking the pee.
Corrected entry: After the stylist kid displays his first designs for the band on the bass guitarist and the drummer, they go to play Zak's song. They start playing in their costumes, but in the next shot, they're in their school uniforms.
Correction: In the first shot, when the kids are still wearing the costumes, Dewey is just beginning to teach them the song, but in the second shot (out of the costumes), all the kids have mastered the song and are playing along, indicating time has passed between the shots (most likely a day or more).
Corrected entry: When Jack Black is having lunch with the other teachers, he puts his fork in his mouth twice, with no food on it either time.
Correction: He is nervously fiddling with the fork because the real teachers are asking him questions that he cannot answer.
Corrected entry: On her first meeting with Dewey, wouldn't Miss Mullins be a little suspicious of the fact that not only has Dewey lost the deep voice that he was using over the phone, but also that he sounds an awful lot like "Mr Schneebly's Roommate?"
Correction: She obviously wasn't suspicious; she desperately needs a teacher and didn't over-analyse. At worst, this is a character mistake.
Corrected entry: In the scene where Dewey is at the bar with the principal, she takes a sip of her beer and Dewey gets up to pick a song. The shot then goes back to the principal to show her taking another "sip" but before she does, you can see that there is already less in the cup than when she put it down. (And I'd assume she hadn't taken another sip while the camera was on Dewey.)
Correction: This isn't true, watch it again, the pint has gone down by the amount she would have drunk.
Correction: The lighting kid mentions earlier in the scene that all the lighting effects are cued to the other song, so the house lighting crew would just have to hit play on the kid's computer.