Cher Horowitz is a wealthy Los Angeles high schooler who lives in a large mansion in Beverly Hills with her father, a successful $500-an-hour litigator. Cher's mother died in a freak accident during a routine liposuction procedure when Cher was just a baby. Her best friend is fellow rich girl Dionne Davenport, who shares Cher's understanding of how it feels to be envied, as well as her passion for fashion.
Cher loves nothing more that to play the matchmaker, and decides to bring two nerdy and low-grading teachers together. Although her initial aim is to soften the teachers so that they will raise her grade, when she sees how happy her matchmaking has made them, she decides to continue doing good works for others. Inspired to give back to the community, Cher adopts a tragically dowdy new girl at school, Tai Frasier. Dionne and Cher give Tai a makeover and groom her for popularity. Tai is enamored of amiable slacker Travis Birkenstock, a skateboarding stoner, but Cher steers her away from him and towards popular snob Elton instead.
This second attempt at matchmaking is nowhere near as successful as her first. Cher's plan backfires completely when Elton rejects Tai and tries to seduce Cher instead. Cher is disheartened and Tai heartbroken at the rejection. While Cher has expressed a marked distaste for "high school boys," she finds herself unexpectedly attracted to a mysterious new student named Christian. In order to get his attention, Cher sends herself flowers and notes. After a few lukewarm dates, Cher is confounded—she can't understand why Christian doesn't like her. Dionne's boyfriend, Murray, eventually explains to Cher that Christian probably doesn't want to date because he is gay. Cher is discouraged, but pursues a friendship with Christian instead.
To add insult to injury, Cher's charitable project with Tai begins to work too well, and Tai's popularity soon surpasses her own. Events reach a crisis point when Cher fails her driving test and cannot "renegotiate" the result. She returns home dejected to find Tai waiting for her. Tai confides that she has become attracted to Cher's step brother, Josh, and wants to enlist Cher's help in dating him. Cher tells Tai that Josh is wrong for her, which prompts a quarrel. Feeling lost and "totally clueless," Cher begins to reflect on her priorities and her desires.
After a great deal of soul searching, Cher realizes that her reaction to Tai's interest in Josh was so vehement precisely because she is interested in him herself. Because Josh is a bleeding-heart liberal, Cher makes rather awkward but heartfelt attempts to live a more meaningful life and show him that she has substantive priorities. She captains the school's Pismo Beach disaster relief effort. Eventually Cher and Josh admit their feelings for each other and kiss.
In a happy ending, the two teachers that Cher set up wed, Cher's friendships with Dionne and Tai are strengthened, Tai and Travis fall in love, and Cher wins a $200 bet when she catches the bouquet at the wedding. As the film closes she embraces Josh.