Dewey Finn (JACK BLACK) has had better days. Patty (SARAH SILVERMAN), the girlfriend to his meek roommate Ned Schneebly (MIKE WHITE), wants him to pay up on his substantial back rent, while his own band has just fired him. Thus, when Dewey takes a call for Ned regarding a substitute teacher opening, the unemployed rocker lies that he's Ned and takes the job.
Arriving at Horace Green Prep, Dewey meets the principal, Rosalie Mullins (JOAN CUSACK), as well as the class of elementary school students. Realizing no one will join his new band, as well as that the students need an awakening in their musical knowledge and tastes, Dewey throws out the current curriculum.
In its place, he teaches all things rock 'n roll to the likes of Zach (JOEY GAYDOS JR.), the lead guitarist; Freddy (KEVIN CLARK), the drummer; Katie (REBECCA BROWN), the bass player; Lawrence (ROBERT TSAI), the keyboardist; singers Tomika (MARYAM HASSAN), Alicia (ALEISHA ALLEN) and Marta (CAITLIN HALE); band stylist Billy (BRIAN FALDUTO), band manager Summer (MIRANDA COSGROVE) and others.
With just weeks to go before the big contest, Dewey tries to whip the kids into shape and hopes that no one discovers his goal or ruse of playing a substitute teacher.