It's the last day of school before summer vacation at Third Street School and fourth-grader T.J. Detweiler (voice of ANDY LAWRENCE) is doing what he does best, namely making the lives of Principal Prickly (voice of DABNEY COLEMAN) and Miss Finster (voice of APRIL WINCHELL) as miserable as possible.
Nevertheless, with the ringing of the afternoon bell, school's out and twelve weeks of goofing off and having fun begins, or so T.J. thinks. Much to his surprise and dismay, his close friends are all headed off to various summer camps. There's Gretchen (voice of ASHLEY JOHNSON), the brainy one who's headed for space camp; Vince (voice of RICKEY D'SHON COLLINS) who's hoping to improve his baseball skills; Gus (voice of COURTLAND MEAD) who's off to a military boot camp; Mikey (voice of JASON DAVIS) who has a great sounding singing voice (courtesy of ROBERT GOULET) and is off to sing with others; and Spinelli (voice of PAMELA SEGALL) who's enthused about attending professional wrestling camp.
Suddenly all alone, T.J. doesn't find much solace from his parents (voices of APRIL WINCHELL & PAUL WILSON) or his older sister, Becky (voice of MELISSA JOAN HART). Yet, when he sees an odd green light emanating from his supposedly closed school and various shady looking characters going in and out of it, the outlook of his summer radically changes.
When neither his family nor the police believe his wild-sounding story, T.J. recalls his friends from camp. They soon learn that Dr. Philliam Benedict (voice of JAMES WOODS), their school's former principal and one-time Secretary of Education, has taken over their school and is using it as his base camp to carry out the cause he's long championed, and that's eliminating summer recess.
As T.J. and his friends discover that Benedict plans to shift the moon in its orbit with his special laser and thus forever eliminate summer, and consequently summer recess, they set out to do what they can to stop him.