In the scene where the principal comes in and observes the class, Dewey improvises a "musical" math lesson, singing things like "9 * 9 = 81" and other very basic arithmetic lessons. But these kids are no younger than 5th grade, and at a fancy prep school they would already be way past those basic skills, yet the principal doesn't even notice. [How someone should or should not react in a given situation is a matter of opinion, and hardly ever movie mistakes. It's entirely possible the principal noticed, but chose not to say or do anything.]

When Dewey and Zack are playing Smoke on the Water for the second time, the positions of their hands are different compared to the first time. [You can easily play the same song with different fingering on a guitar. Any guitarist will tell you this.]

Battle of the Bands is performed once a year. Dewey taught for only a month. It isn't possible for Battle of the Bands to be only a month after the last one. [There's no problem here. The first concert we see Dewey in, is a regular gig, not a Battle of the Bands. There is nothing to suggest that less than a year has gone since the last time the Battle was held, as we do not see or hear of this on screen.]

The timing of the day of Battle of the Bands is very suspect. It has to be first thing in the morning, say 9:00 at the latest, because all the parents are in Principal Mullins' office demanding to know why she hadn't caught on to Dewey's fraud, and the new substitute for the kids hasn't arrived yet. Yet when they get to the performance venue, there's barely enough time for them to get ready and go on stage as the last band to perform. Allowing travel time and the time it took to pick up Dewey, it still can't be much past 10:00 AM. It's too hard to believe that a bunch of hard-rockers would be up that early to watch all those bands and that everything would essentially be over by that time. [We simply have no way of knowing what time it is, it's pure speculation that all parents would be available at 9am. The best indication of time is that when Dewey leaves the apartment, Ned and his girlfriend are coming home, presumably from work, which would suggest that it is late afternoon at least.]

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?" [She obviously wasn't suspicious, she needs a teacher and didn't over analyse. At worst this is a character mistake.]

When Dewey is getting ready for teachers night and Ned opens the check and finds out Dewey's secret. Dewey admits to Ned that he took a job as him and told him how the kids rock, he then talks about Lawrence on keyboards but calls him "Larry". [Larry is the common nickname for people named Lawrence.]

When Dewey first asks the principal how much the job pays she says $650 a week. When Ned receives a check in the mail it is for $1200. The check should be for $1300 which would be for two weeks pay. [$100 in taxes were withheld.]

When Rosalie walks into the staff room to tell the teachers that it's parents' night, the camera shows her walking into the center of the room. In the face on shot, however, she is talking in the door way. [Rosalie enters the room, but does not move to the center. She stops directly alongside the librarian in the blue chair. She remains in this position for the entire shot.]

How did the people who were running the Battle of the Bands know they were the school of rock? The girls made up the name after the audition. [Dewey could've called Battle Of The Bands organizers and told them that they were the School of Rock before the day.]

This isn't technically a mistake within the film, but it's interesting. The official title of the film is "School of Rock," yet in the opening credits, the title reads as "The School of Rock." [If you listen to the commentary with the director they say that they were having trouble deciding what the movie would be called. At the last moment they changed it from "The School of Rock" to "School of Rock". They had already filmed the beginning and didn't get to fix it.]

When Zack picks up the electric guitar for the first time in the movie, Dewey plays 'Smoke on the Water' and we hear some sort of noise made by Dewey vocally. However, his mouth is constantly firmly shut, and this noise could not have been made unless he opened his mouth. [It is actually very possible to make this noise with your mouth closed, because I have tried it myself. The sound comes from your throat and you can hear it if your mouth is open or not.]

During the scene when the Principal is coming to the class, the students hurry up and put everything away. When the kids are putting the drum set away they never put the high hat away. It just seemed to disappear. [no, they just don't SHOW the high hat being put away. Someone might have been doing something with the high hat, then, when they had to pack everything away, they could have put it in the cupboard after the drums.]

When Dewey is handing out the CDs as homework, he gives Lawrence the 'Yes' CD. However, at parents evening, Lawrence's father says "How is this homework?" and holds up a Pink Floyd CD. [Since the Parents' Night and the day that Dewey assigned the 'Yes' CD to Larry are farther apart then one night, we can assume that Dewey could have given Larry another CD for homework in-between these two times.]

When "Fancy Pants" shows Jack, Freddy, and Kaity's new outfits, Jack hears Zack playing a song. He tells the band to come over and play it. Freddy and Kaity come over in their outfits, but when they start to get more into the song, they're now wearing their school uniforms. [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).]

After lunch, in the scene where Jack Black gives the kids their roles in the band and they're lined up against the wall, the desks are together. Prior to lunch the desks were apart and you could walk between them. After the scene, the desks are apart again. [It's not impossible that they moved the desks before they lined up and moved them back again after the 'exercise' was completed, surely? My teachers got us to do it all the time.]

In the scene where the children are dying of a rare blood disease, Freddy is lying on the ground. Then it skips back to Dewey talking to the talent director for the "Battle of the Bands." When Dewey is walking out of the building he says, "We're on the bill," but you see Freddy standing up jumping, how could he be standing up before he knew he was on the bill. [Freddy wasn't jumping up and down. He was hanging on the van, and he jumped off it when Dewey said they were on the bill.]

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? [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.]

In the scene where the class is saying their version of the Pledge of Allegiance, the camera zooms in on a blonde-haired girl. If you look at the girl's hand, you'll notice she has the wrong hand on her chest. (It should be her right hand, so is it over her heart). [It was intentional, just like when the kids were saluting Dewey; some kids had their right hands up, while others had their left hands up.] [actually if you look at the girl at other parts during the 'pledge' she has her hand over her heart so it really was a mistake. She changed her hands around.]

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. [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.]

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.) [This isn't true, watch it again, the pint has gone down by the amount she would have drunk.]