Rock band No Vacancy performs at a nightclub three weeks before auditioning for a Battle of the Bands competition. Guitarist Dewey Finn creates on-stage antics, including a stage dive that abruptly ends the performance. The next morning, Dewey wakes in the apartment he lives in with Ned Schneebly and his girlfriend, Patty Di Marco. They inform Dewey he must make up for his overdue share of the rent or move out. When Dewey meets No Vacancy at a rehearsal session, he finds out that he has been replaced by another guitarist named Spider. Later, while attempting to sell some of his equipment for rent money, Dewey answers a phone call from Rosalie Mullins, the principal of the Horace Green prep school, inquiring for Ned about a short-term position as a substitute teacher. Desperate for rent money, Dewey impersonates Ned and gets the position. On his first day at the school, Dewey adopts the name "Mr. S" and spends his first day behaving erratically, much to the class' confusion.
The next day, Dewey overhears the students playing their instruments in music class and devises a plan to form them into a new band to audition for Battle of the Bands. He casts Zack Mooneyham as lead guitarist, Freddy Jones as drummer, cellist Katie on bass, pianist Lawrence on keyboard, and himself as lead vocalist and guitarist. He assigns the rest of the class to various roles of backup singers, groupies, roadies, with Summer Hathaway as band manager. The project takes over normal lessons, but helps the students to embrace their talents and gain confidence. He reassures Lawrence, who is worried about not being cool enough for the band, Zack, whose overbearing father disapproves of rock music, and Tamika, an overweight girl who is too self-conscious to even audition for backup singer despite an amazing voice. During one eloquent lesson, he teaches the kids that rock and roll is the way to "Stick it to the Man" and stand up for themselves. Band "groupies" Michelle and Elena, with Summer's approval, pitch the band name "The School of Rock."
Two weeks into his hiring, Dewey sneaks some of his students out of school to audition for a spot in the competition, while the rest of the class stay behind to maintain cover. When Freddy wanders off, Dewey retrieves him, but the group is rejected because the bill is full. After Summer tricks the staff into thinking that the students all have a terminal illness, the band is nevertheless auditioned. The next day, Mullins decides to check on his teaching progress, forcing Dewey to teach the actual material. Mullins explains that a parents' night will take place at the school the day before Battle of the Bands.
As Dewey prepares for the parents' night, Ned receives a paycheck from the school via mail, and eventually learns of Dewey's treachery. During the parents' meeting, the parents inquire about what Dewey was teaching the kids. The meeting is halted when police, Ned, Patty, and Mullins arrive. Dewey reveals his treachery and abruptly leaves. Back at the apartment, Dewey and Patty clash, while Ned intervenes and informs Dewey that he should move out.
The next morning, the parents go on an uproar in front of Mullins at her office, while the kids decide not to let their hard work go to waste. When the new substitute discovers that the kids are missing, she informs Mullins, and Mullins and the parents race to the competition. Ned, constantly bossed around by Patty up to this point, finally stands up for himself by breaking up with Patty and leaves to see the band perform. A school bus comes to pick up Dewey, who leads the kids to the Battle of the Bands, and decides that they should play a song written by Zack. Initially dismissed as a gimmick, the band wins over the entire crowd. Much to Dewey's dismay, No Vacancy wins, but the audience chant for School of Rock and demand an encore. Mullins and the parents, while upset at the deception, admit to being impressed by the children's talent and confidence on stage.
Some time later, an after school program known as the School of Rock has opened as Dewey continues to coach the students he played with before while Ned teaches beginners.
- Jack Black as Dewey Finn
- Joan Cusack as Principal Rosalie "Roz" Mullins
- Mike White as Ned Schneebly
- Sarah Silverman as Patty Di Marco
- Miranda Cosgrove as Summer "Tinkerbell" Hathaway
- Joey Gaydos Jr. as Zack "Zack-Attack" Mooneyham
- Kevin Clark as Freddy "Spazzy McGee" Jones
- Rebecca Brown as Katie "Posh Spice"
- Robert Tsai as Lawrence "Mr. Cool"
- Maryam Hassan as Tomika "Turkey Sub"
- Aleisha Allen as Alicia "Brace Face"
- Caitlin Hale as Marta "Blondie"
- Brian Falduto as Billy "Fancy Pants"
- Zachary Infante as Gordon "Roadrunner"
- James Hosey as Marco "Carrot Top"
- Angelo Massagli as Frankie "Tough Guy"
- Cole Hawkins as Leonard "Short Stop"
- Jordan-Claire Green as Michelle
- Veronica Afflerbach as Eleni
- Adam Pascal as Theo
- Lucas Babin as Spider
- Pierre Leen as Neil
- Shawn Rodney as Shawn