Lloyd Christmas (ERIC CHRISTIAN OLSEN) and Harry Dunne (DEREK RICHARDSON) aren't the brightest bulbs in the universe, or even their high school where they meet. Harry has been home schooled by his mom (MIMI ROGERS), while Lloyd actually lives in the high school with his custodian dad, Ray (LUIS GUZMAN), but still goes outside to catch the bus back to where he just left.
Little do they know that Principal Collins (EUGENE LEVY) and his lover, lunch lady Ms. Heller (CHERI OTERI), have conspired to use the two as the basis for a special needs class. Collins hopes to pocket the promised $100,000 grant money for himself, with Heller serving as their teacher and encouraging them to recruit other students for their class.
Among those chosen is Turk (ELDEN HENSON), the class bully; Carl (WILLIAM LEE SCOTT) the football player; Lewis (SHIA LaBEOUF) who works as a costumed mascot; skateboarder Toby (JOSH BRAATEN); his new girlfriend Terri (TEAL REDMANN) and foreign student Ching Chong (MICHELLE KRUSIEC). None is mentally slow, but they join the class since it means they won't have to do any regular schoolwork.
However, school newspaper reporter Jessica Matthews (RACHEL NICHOLS) becomes suspicious of the class and Collins' activities. With the purposeful and accidental help from Lloyd and Harry, she then sets out to expose the corruption and ruse.