Harry Dunne, played by Derek Richardson, has spent his entire life being homeschooled by his mother, Mrs. Dunne (Mimi Rogers). Now, he finally has the opportunity to attend a regular school. Simultaneously, another character, Lloyd Christmas, portrayed by Eric Christian Olsen, embarks on his journey as he seeks a place in the school after being adopted multiple times and finally settling with Ray, the school janitor (Luis Guzman). Eager to integrate with regular students, Lloyd decides to join Harry on his school adventure.
As fate would have it, while Harry is on a mission to uncover a treasure his mother has tasked him with finding, he bumps into Lloyd, who accidentally chips a tooth during their encounter. Their instant chemistry leads to a remarkable friendship where they travel to school together. Harry finds himself smitten with Jessica, who captivates him with her short skirt, tight sweater, and a mischievous air of allure.
Lloyd also introduces Harry to his so-called 'friend', Turk (Elden Henson), the school bully who relishes tormenting Lloyd's life—even though Lloyd seems to take it in stride. Their first encounter leads to Turk unceremoniously stuffing Lloyd into a dustbin and hoisting both boys up a flagpole, all the while making it clear that he won't tolerate Harry's budding relationship with Jessica.
Meanwhile, the duplicitous Principal Collins, embodied by Eugene Levy, is on a mission to acquire enough funds to secure a luxurious condominium in Waikiki for himself and his girlfriend, Ms. Heller (Cheri Oteri), who works as the cafeteria lady. Upon witnessing the spectacle of the two boys stuck on the flagpole, he concocts a nefarious scheme. Collins decides to exploit the system by creating a 'special needs' class, brilliantly aiming to swindle $100,000 from a grant designated by former special needs student Richard Moffit, who has since achieved great success.
As Harry and Lloyd are drawn into this dubious undertaking, they enthusiastically sign up students who are deemed 'different' for the special needs class. This eclectic group includes Turks (who reluctantly signs up), a teen named Toby (Josh Braaten) with a broken leg who believes the class will offer him a break from homework, and many others, each with their own quirks. Among them are geeky Lewis (Shia LaBeouf), who Harry and Lloyd mistakenly think could be a centaur, and Cindy (Michelle Krusiec), an Asian exchange student who eventually becomes Turk's girlfriend.
Enter Jessica, a determined student who senses something amiss with Collins' sudden enthusiasm for the special needs initiative. Despite Ms. Heller's attempts to steer her away from uncovering the truth, Jessica's curiosity leads her to gather evidence. In a comedic turn of events, Harry interprets Jessica's friendship as romantic interest and, seeking courtship advice from Lloyd, prepares a disastrous chocolate bar gift that leads to a chaotic bathroom mishap at Jessica's house, further complicating the dynamics between the trio.
Tensions rise between Harry and Lloyd as their friendship is tested over Jessica, but they reconcile when they realize their bond is irreplaceable, particularly after a series of misunderstandings including a stuffed polar bear stolen during a school field trip.
Principal Collins' scheme falls apart when Harry and Lloyd discover the damning evidence intended to blackmail Jessica. As they rally their special needs class to expose Collins' deceit during the Thanksgiving Parade with a float depicting him, they skillfully broadcast the recordings incriminating him and Ms. Heller.
Ultimately, their actions lead to the arrest of Collins and Ms. Heller, much to Jessica's appreciation. Despite their heroics, they quickly find out that Jessica has a boyfriend and, whilst they vow to prioritize their friendship over romantic pursuits, they are soon entangled in another confusing situation with two new girls in a flashy red Ferrari. The mud-splashing antics mark yet another lighthearted conclusion to their misadventures, showcasing the antics and chaos that define their high school experience.
