Zack Siler is the big man on campus at his Southern California high school. After returning from spring break, he finds out his girlfriend, Taylor, has cheated on him with a reality TV star, Brock. After Zack and Taylor's breakup, Zack consoles himself by claiming that Taylor is replaceable with any girl in the school. Zack's friend Dean disagrees and bets Zack to turn any random girl from school into the prom queen in six weeks. Zack accepts, and Dean chooses Laney Boggs, an awkward and unpopular art student.

Zack attempts to befriend Laney, but she pointedly ignores his advances until he asks for her help with art. She reluctantly invites him to a small theater lounge where she will perform. Intending to deter him, Laney volunteers Zack to perform onstage. Zack manages to improvise a routine with his hacky sack. Laney is impressed but still rejects him when he attempts to charm her again.

When Zack shows up at her house, Laney reluctantly agrees to go to the beach with him and his friends, and they invite her to a party later. Laney says she's busy, but Zack persuades her to go. He enlists his sister, Mack, to give her a makeover. At the party, Taylor, who is embarrassed by Brock and jealous of Laney, publicly humiliates Laney and brings her to tears.

Laney is surprised to be nominated for prom queen, along with Taylor. Zack then goes by Laney's house and asks about her mother, who died when Laney was young, and talks about his father, who is pressuring him to go to Dartmouth for college. Zack leans in to kiss Laney but pulls back when she jokes that it's just to get her vote for prom king.

The next day, Zack defends Laney's brother, Simon, from bullies in the cafeteria. After a falling out with Zack, Dean asks Laney to be his prom date. Taylor is humiliated when Brock dumps her, so she cozies up to Zack. When Zack turns her down, she tells him that Dean has already asked Laney to the prom. When Zack confronts him, Dean reveals the bet, forcing a public confession from Zack. A furious Laney rushes from the room, refusing to speak to Zack.

Unable to reconcile with Laney, Zack takes his sister to the prom. After some persuading from her father, a disheartened Laney agrees to go with Dean. At the dance, Dean boasts of his plan to seduce Laney. Laney's friend Jesse overhears, and he and Mack rush to warn Zack, who has taken the stage with Taylor as Prom King and Queen. Zack rushes after Laney, who's already left with Dean.

Laney returns home to find Zack there. Laney explains how she avoided Dean's advances. Zack confesses his true feelings, and they share a dance and kiss by the pool. When Laney asks Zack about the bet, Zack says he will honor the terms, which entail appearing nude at the graduation ceremony.