Max Keeble, a young paperboy, is getting ready for his first year in middle school, and he wishes to become cool after being a nerd in previous years. He constantly faces off against Evil Ice Cream Man, who pretends to be a bionic supervillain while he is really just a cheap ice cream man. The principal, Elliot Jindrake, hates children and plots to demolish Max's beloved animal shelter so that he can become the next chairman after the current one, "Crazy Legs", retires. Max, alongside his best friends Megan and Robe, are frequently bullied by childhood friend Troy McGinty and former millionaire Dobbs.
Max' father, Don Keeble, acts in embarrassing commercials, but he gets a promotion eventually. This forces his family to move to Chicago in a week. Max steals a metal coil from Evil Ice Cream Man's truck, places it in Dobbs' briefcase, steals Dobbs' handheld, and frames Evil Ice Cream Man for it. Evil Ice Cream Man is hated and insulted by young customers, and his ice cream begins to melt. He hears that it was Dobbs' fault, and when Dobbs confronts him about stealing his handheld, they insult each other by destroying the items. Max framed Evil Ice Cream Man for setting up Dobbs, and their hate resumes.
Troy gets rid of Max due to fear that he is the next target. Elliot blames Max and is very hard on him. Troy, just like he thought, is the next target. He was once scared of a cartoon frog, MacGoogles, and is now terrified. Max plays the theme song in the science room across from Troy's locker, scaring Troy slightly. He then gets MacGoogles to trap Troy in the gym, where he is found by a sports coach. Troy overcomes his fear. Max puts animal food in Jindrake's breath mints, making the animals from the animal shelter go near Jindrake's mouth. He then hosts a food fight.
Don quits his job and Max stays home, unknown to him, who goes to a milkshake party that is hosted by his love interest, Jenna. Megan and Robe are suffering because of the vengeance methods that Max unleashed. Megan, Max, Robe, and the rest of the school gather around Troy and Dobbs, trapping them. Both Dobbs and Troy try to place the blame on each other, making them both angry. The others take back the school. Max picks up Dobbs and Troy and throws them in the dumpster together. Evil Ice Cream Man is left unharmed. Jindrake's new basketball court, which he was building over the animal shelter, is ruined and the bulldozers pursue him. He is then fired when his plot of fiddling with the school budget is exposed by Max. Evil Ice Cream Man closes in on Max as the film ends.
- Alex D. Linz as Max Keeble
- Zena Grey as Megan
- Josh Peck as Robe
- Noel Fisher as Troy McGinty
- Robert Carradine as Don Keeble
- Nora Dunn as Lily Keeble
- Jamie Kennedy as Evil Ice Cream Man
- Larry Miller as Principal Elliot T. Jindrake
- Orlando Brown as Dobbs
- Justin Berfield as Caption writer
- Brooke Anne Smith as Jenna
- Myra as Chelsea
- Kyle Sullivan as Techie kid
- Tony Hawk as himself (cameo)
- Lil' Romeo as himself (cameo)
- Clifton Davis as Superintendent Bobby "Crazy Legs" Knebworth
- Amy Hill as Ms. Phyllis Rangoon
- Amber Valletta as Ms. Dingman
- Martin Spanjers as Runty Band Member
- Adam Lamberg as Student on Motorcycle
- Countess Vaughn as Office Admin. Assistant
- Dennis Haskins as Mr. Kohls