After Napoleon and Kip's grandmother breaks her coccyx riding an ATV at the sand dunes, Uncle Rico arrives to look after them while she is in the hospital. Uncle Rico proceeds to have an indirect chaotic effect on Napoleon's life: he succeeds in getting Napoleon a date for the high school dance by eliciting sympathy from the mother of the girl Napoleon asked to the dance, Trisha; he makes Napoleon look foolish at school by asking two of Napoleon's schoolmates to hand out organic breast-enlargement flyers (which they later post on his locker as a prank); and he also nearly ruins Napoleon's relationship with his new friend Deb by giving her the same flyer, claiming that Napoleon suggested it. Uncle Rico also affects Kip's life by involving him in his business ventures, enabling Kip to raise enough money to pay for his internet girlfriend, LaFawnduh, to visit him. Napoleon is driven to anger, and attempts to kick Uncle Rico out of the house. This is obviated when Napoleon's grandmother comes home, and Uncle Rico returns to his orange camper van in an empty field. Rico is beaten up by Rex, who owns the "Rex Kwon Do" dojo--probably a parody of the McDojo phenomenon--seen earlier in the movie, for attempting to sell his wife, Starla, a breast enhancement supplement known as "Bust Must +".
The final plot-point involves Napoleon and Pedro, with some help from Deb, attempting to get Pedro elected class president. Pedro opposes Summer, who is expected to win. Summer's campaign consists of handing out flyers and badges, while Napoleon and Pedro counter by posting flyers drawn by Napoleon, holding a piñata competition—with the piñata made in the image of Summer herself, handing out boondoggle key chains made by Deb, and offering protection from Pedro's two intimidating older cousins against school bullies. The final sequence involves the closing speeches made by each presidential candidate, and the candidate's skits that follow. Summer goes first and attempts to bribe the audience with promises such as installing two soda machines in the cafeteria. She and the "Happy Hands Club" (without Napoleon, who is also a member) perform a short dance for their skit. Pedro makes a short monotone speech, promising more worthwhile but less exciting things, and uses Napoleon's advice when he concludes with the statement, "If you vote for me, all your wildest dreams will come true." Pedro walks slowly off of the stage, and does not return for a skit as he did not have one prepared, as he did not realize one was required until a school staff member informed him immediately before his speach.
A couple of days earlier, while browsing a second-hand store, Napoleon had found a D-Qwons Dance Grooves video and learned the moves. When LaFawnduh meets Napoleon, she gives him an unlabeled cassette tape (which contains Jamiroquai's "Canned Heat"). After Pedro's speech, Napoleon gives the tape to the sound technician for the skit, and walks on stage. Napoleon performs a dance routine, earning a standing ovation from the student body.
The film ends with a montage of each character that ties up all narrative threads. Uncle Rico ends up living in the field in his van as he was first seen, and a woman, his ex-girlfriend referred to earlier in the movie, approaches on a bicycle. Kip and LaFawnduh are seen getting on a bus heading out of the town. Pedro is elected president and is seen at a congratulatory party with his family. Napoleon's grandmother returns healthy. The final shot is of Napoleon and Deb playing tetherball together. In the post-credits scene, Kip and LaFawnduh are married, and Napoleon rides up on a "wild honeymoon stallion", which he claims to have just tamed. The couple gets onto the horse and ride away, and Napoleon exclaims "Lucky!"