A troll hates pranking people and is teased so much, he runs away. When a park ranger starts capturing the other trolls, the outcast troll has to rescue his friends and family without pulling any pranks.
Dropout and school district employee Ernest Worrell (Jim Varney) is in danger of losing his job because of a new rule that says all workers must be high school graduates. Ernest enrolls in classes, but the lovable dimwit struggles to retain information -- until teachers Gerta (Linda Kash) and Bobby (Bill Byrge) subject him to scientific experiments that turn him into a genius. Suddenly smart, Ernest also becomes an egomaniac, and unless he's careful he'll drive away his pals.
While divorced and bickering grandparents watch their grandchildren (Tia Mowry, Tamera Mowry), a lab experiment gone awry transforms the elders into teenagers again.