Guitarist Dewey Finn is voted out o

Guitarist Dewey Finn is voted out of his local rock band, No Vacancy, when his on-stage antics unnerve the other band members. Dewey's roommate, Ned Schneebly, pressured by Ned's girlfriend Patty Di Marco, threatens to evict Dewey without a paying gig as he has been late on his rent. Some time later, Dewey takes a call for Ned from a nearby prestigious private preparatory school, who are looking for an immediately short-term substitute teacher. On hearing how much the teaching job pays, Dewey feigns himself as Ned and takes the job.

Dewey meets Principal Rosalie "Roz" Mullins, and is introduced to the class. With no teaching experience, Dewey instructs the class to do use his time freely when not in other studies. He overhears the class in their music studies and observes that they are competent performers, and hatches a plan to recruit the students as part of his new band as to compete against No Vacancy at an upcoming battle of the bands event. Secretly, he starts teaching many of the students on various instruments and the methods of classic rock, while having other members of the class act as groupies to help maintain the illusion that Dewey is actually teaching them. Through this, he helps several of the students gain confidence in their musical skills. He also befriends Rosalie, as to help secure the band's performance under the guise of a school field trip. At the audition for the battle, Dewey has to chase down and talk to several of the students when they go awry, causing them to miss the audition period. However, the other students come up with a plan to convince the judging panel to let them in.

Dewey learns that parent-teacher conferences are scheduled for the night before the battle of the bands. On the day of the conference, Ned discovers a check addressed to him from the school, and attempt to call, forcing Dewey to explain the situation, unaware Patty is also in the apartment. That night, Dewey is convincingly telling the parents about their students' performance in class when the police arrive, alerted by Patty. Dewey is immediately ejected from the school and goes home to get drunk and sulk.

Principal Rosalie does not want to let the field trip go to waste as planned, and prepares to send Dewey's class to a fine arts performance as a show of good will to the upset parents. The students are able to convince the bus driver to take them to get Dewey before Rosalie and the other parent chaperons get on the bus. They wake Dewey and collect their instruments and set off for the show. Ned, also interested in seeing Dewey perform and recalling his own music past, goes as well against Patty's wishes. Rosalie and the parents then discover the students missing and race to the battle of the bands as well.

Dewey and the students take the stage as the band "School of Rock" as the parents file into the venue. They play a song that is well received by the crowd, with Rosalin and the parents recognizing the talent in their students that Dewey has showed them. Though No Vacancy still wins the battle, the audience cheers for School of Rock to do an encore performance. Some time later, Dewey and Ned have worked together to open an after-school program to continue to teach rock music to the students as well as newer students just starting on instruments.