The protagonist of the film and musical, he's a talented but lazy musician who slacks off his former band-mate Ned. When he's kicked out from his band No Vacancy and is overdue with his share of the rent, in order to find a job he takes up an offer for substitute teacher intended for Ned. Impersonating Ned, he decides to form a rock band from his class and compete in a Battle of the Bands, to win the cash prize and clear his debt. However, when confronted with the reality of teaching he starts to become the mask.
- Brilliant, but Lazy: At the start of the film he seems nothing more than a self-centered slacker, but he's actually a competent guitarist and displays extensive and accurate knowledge of modern music.
- Character Development: From obnoxious freeloader slacker to Team Dad Cool Teacher.
- Cool Teacher: A Reconstruction. Initially, he's obviously incompetent when confronted with a class of kids to teach, and the kids themselves don't hold him in much esteem and see his "classes" as an excuse to do nothing. As the story goes on and Dewey's qualities begin to emerge, he gets genuinely interested in the class' welfare as they get interested in the band project. In the epilogue he becomes a real teacher, of an after-school music program.
- Demoted to Extra: He's a supporting character in the TV series, thanks to the focus being more on the kids.
- Dumbass Has a Point: He accurately tells Freddy that "Rock ain't about gettin' loaded and acting like a jerk."
- Earlier when he tells Patty that being a rock musician wasn't easy, stating "Rockin' ain't no walk in the park, lady!"
- Face of the Band: In-Universe, he originally conceives the School of Rock project as a way to create himself a backing band to win the Battle of the Bands. He keeps the role at the final performance at the kids' insistence.
- The Heart: While Dewey was a lying, self-centered jackass who saw the kids as a means to snub his former band, he became a caring, charismatic teacher. He helps Zach, Lawrence, and Tomika with their self-esteem issues and helps Freddie find something he wants to learn and is genuinely passionate about.
- Heterosexual Life-Partners: With Ned.
- Hidden Depths: As immature as he is, he takes his ambitions to become a rock star completely seriously, as evidenced by his use of theory terms when teaching the kids "Smoke On The Water."
- Jerkass Has a Point: He may be a slacker and a mooch, but his dislike of Patty is rather understandable, given she's a domineering jerk who frequently talks down to Ned.
- He later calls her out for calling the cops on him at the school, not for his sake but for the kids, in that he wasn't able to tell the parents how great their kids were at music once the police outed him.
- Jerk with a Heart of Gold: He has been mooching off Ned for years and has no desire to get a real job. He also impersonates Ned just to he can avoid getting knocked out, which comes back to bite him later. However he's still a good friend to Ned by promising to pay him the money he owes him and urges him to dump Patty (for Ned's sake as well as his own), brings out the musical talent in the kids he teaches, tries to sort out some of their self-esteem issues and apologizes to the kids later that he used them for his own means.
- The Nicknamer: He gives a nickname to each one of the kids in his class.
- No Celebrities Were Harmed: A hard rock lead guitarist dressed in a schoolboy's uniform. Somewhat Justified in that the whole band is school-themed.
- Only Known By His Nickname: On his first day as teacher, he tells the kids to call him "Mr. S". This is because he doesn't know how to spell "Schneebly".
- Papa Wolf: When Freddy wanders off to mingle with some suspicious dudes, Dewey gets extremely worried and drags him away pronto.
- The Slacker: He starts the film as a recently unemployed, ne'er-do-well who is several months behind with his share of the rent.
- Team Dad: He eventually becomes this for Class 21-B, by teaching them not only music but the importance of self-worth and self-determination. At the final performance there's a strong bond of mutual respect between him and the kids.
- Took a Level in Kindness: The School of Rock project allows him to demonstrate his better Team Dad qualities.
Principal Rosalie "Roz" Mullins
The principal of the stuffy Horace Green prep school.
- All Girls Want Bad Boys: She has Ship Tease with Dewey in the bar scene, and she's seen flirting with Spider at the Battle of the Bands.
- Broken Smile: When she cheerfully informes the parents that all their children have gone missing.
- Defrosting Ice Queen: Getting to know Dewey allows her to let loose and have fun more, culminating in her genuinely enjoying the kids' performance at the end of the film.
- Hard-Drinking Party Girl: She acts as this in the pub scene, courtesy of some beer and "Edge of Seventeen" as BGM.
- Promoted to Love Interest: Dewey's, in the musical.
- Running Away to Cry: A variation: after she's overwhelmed by the parents' indignation, she excuses herself, goes to the stairwell and makes herself stand in a corner in shame.
Dewey's roommate, former band-mate and best friend. He was meant to be the substitute teacher at Horace Green until Dewey takes the call and steals his identity.
- Adapted Out: From the TV series.
- Bros Before Hoes: At the end of the film, he continues his friendship with Dewey and breaks up with Patty.
- Friend Versus Lover: He's caught in the midst of Dewey and Patty's mutual hatred. When Dewey goes to play at the Battle of the Bands, he's conflicted about going to see him or ignoring him as demanded by Patty. He goes, slamming the door in Patty's face.
- Henpecked Husband: Well, boyfriend, but he's still an absolute pushover compared to Patty.
- Heterosexual Life-Partners: With Dewey.
- Nice Guy: Unlike his ex-girlfriend, he's much nicer.
Patty Di Marco
Ned's overbearing girlfriend.
- Adapted Out: From the TV series, just like Ned.
- Jerkass: She's mean, rude and constantly talking down to Ned. She also generally berates and bullies Dewey
- Jerkass Has a Point: While she might be a massive jerk, she's not wrong about being angry at Dewey for abusing his friend's kindness to live rent free in their apartment while refusing to get a job. Furthermore, she's not wrong to be angry that Dewey's response to Ned finally trying to make Dewey pay the rent he owes was to impersonate Ned, committing fraud and possibly putting Ned's job in jeopardy while also originally not caring about the quality of education he was giving the kids.
- Hate Sink: She's very abusive towards Ned.
- Hoist by His Own Petard: She spends the entire film nagging Ned to stand up for himself. By the end, he does - by dumping her.
- Hypocrite: She's annoyed with Dewey for taking advantage of Ned, but she walks all over him just as much.
Dewey's former band, who fired him when his antics proved to be in the way of success.
School of Rock
The class of Horace Green which Dewey ends up teaching. He decides to make them into the eponymous School of Rock band, assigning them not only actual performing duties but all other tasks connected to a live show.
- Child Prodigy: A whole class of them. Not only are there enough kids who can sing or play an instrument at an almost professional level, but there are also costume designers (Billy), computer/digital design experts (Gordon), a scarily hypercompetent manager (Summer), and so on.
- Fat and Skinny: The two kids in charge of security: Tough Guy is a tall, large white kid, while Short Stop is tiny, thin and black.
- Graceful Loser: Despite losing the Battle of the Bands to No Vacancy, the kids are nevertheless overjoyed for the amazing experience. It helps that they won the adoration of the public.
- Groupie: Michelle and Eleni, though (thankfully) a PG-13 variant: they are tasked with merchandise and branding, including naming the band.
- The Roadie: Gordon and Marco, though since the band doesn't actually tour, they are in charge of logistics, equipment and SFX.
Summer "Tinkerbell" Hathaway
The class factotum who gets assigned the role of band manager.
- Defrosting Ice Queen: She gets on board with the "School of Rock" project in the hope of getting good marks and/or experience for her résumé, but later on she becomes genuinely invested in the band.
- Hollywood Tone-Deaf: She asks Dewey to put her in the band as singer, and to prove her "ability" she sings a couple of lines from "Memory". Dewey immediately tells her he doesn't want to hear that song ever again.
- Hilariously, Miranda Cosgrove is actually a decent singer, and she had to be coached how to sing badly for this gag.
- Hypercompetent Sidekick: The smart and methodical band manager to Dewey's rambunctious Face of the Band.
Freddy "Spazzy McGee" Jones
The band's drummer.
- All Drummers Are Animals: Downplayed in the actual performance, but he's the most rebellious kid in class.
- The Artifact: His nickname of "Spazzy McGee" relates to a previous version of the film script, where he would have had ADHD and constantly assuming pills.
- Race Lift: Caucasian in the film but Latino in the TV adaptation.
Zack "Zack-Attack" Mooneyham
The band's lead guitarist and composer.
- Asian and Nerdy: Downplayed in the TV series, where the "nerdy" part is mostly limited to his good grades.
- Race Lift: In the TV series he goes from Caucasian to Asian, curiously swapping ethnicities with Lawrence.
- "Well Done, Son!" Guy: His main conflict stems from his father not accepting Zack's passions, especially in the musical where the father is portrayed as a disinterested workaholic. For that matter, at the final performance his father looks legitimately proud of Zack.
Katie "Posh Spice"
The band's bassist.
- Adapted Out: She's absent from the TV series, her role as bassist given to Tomika.
- Nobody Loves the Bassist: On a meta level: she's the only major band member who doesn't have a solo in the final performance in the film, one of two (along with Lawrence) who doesn't have a subplot in the musical, and she's been Adapted Out from the TV series.
Lawrence "Mr. Cool"
The band's keyboardist.
- Asian and Nerdy: He's self-aware about his appearance and confides to Dewey that he doesn't feel at ease in the band, because he doesn't see himself as "cool".
- Race Lift: In the TV series he goes from Asian to Caucasian, curiously swapping ethnicities with Zack.
- Hidden Depths: He wants to be accepted by his peers
Tomika "Turkey Sub"
A shy, overweight girl who eventually becomes co-lead singer.
- Amazing Freaking Grace: In the musical, she belts out "Amazing Grace" to demonstrate her singing.
- Appearance Angst: She's self-conscious about her weight and almost pulls out from her singer role. Dewey gives her a pep talk, recalling talented, Big Beautiful Women like Aretha Franklin.
- Composite Character: In the TV series, she handles the bass like Adapted Out Katie does in the film.
- Has Two Daddies: In the musical, she's the daughter of a gay couple.
- Lead Bassist: In the TV series she's the bassist and lead vocalist.
- New Transfer Student: In the musical, her shyness derives from being a transfer student with no friends at Horace Green rather than her appearance.
- Shrinking Violet: Despite having a phenomenal singing voice, she doesn't initially answer Dewey's call for backing singers because she's self-conscious about her appearance.
Billy "Fancy Pants"
The stylist for the band's members.
- Camp Gay: A feminine boy who listens to Liza Minnelli and is in charge of the band's costumes. As a child, his sexuality isn't explicitly addressed but the trope is blatant. Reportedly, these traits were amplified for comedy by director Richard Linklater, and as a consequence screenwriter Mike White (who is bisexual and has a gay father) disowned the film.
- Gender Normative Plot: Thanks to Adaptation Expansion in the musical, he's given his own subplot concerning the long line of manly football players in his family and his refusal to be one as well.
- Queer Character, Queer Actor: Brian Falduto would later come out as gay.