Andrew Lawrence as T.J. Detweiler (voice)

Rickey D'Shon Collins as Vince La Salle (voice)

Pamela Adlon as Spinelli (voice)

Ashley Johnson as Gretchen Grundler (voice)

Jason Davis as Mikey Blumberg (voice)

Courtland Mead as Gus Griswald (voice)

April Winchell as Ms. Finster / Mrs. Detweiller (voice)

Dabney Coleman as Principal Peter Prickly (voice)

Ryan O'Donohue as Digger Dave / Randall (voice)

Robert Goulet as Mikey's Singing Voice (voice)

Melissa Joan Hart as Becky (voice)

Peter MacNicol as Fenwick (voice)

Tony Jay as Dr. Rosenthal (voice)

James Woods as Dr. Phillium Benedict (voice)

Andrea Martin as Lunchlady Harriet (voice)

Tress MacNeille as Lunchlady Irma / Ms. Lemon / Opera Director / Dr. Steinheimer (voice)

Nicholas Turturro as Cop #1 (voice)

Kevin Michael Richardson as Cop #2 (voice)

Dan Castellaneta as Guard #1 (voice)

Diedrich Bader as Guard #2 (voice)

Kath Soucie as Counselor (voice)

Charles Kimbrough as Mort Chalk (voice)

Robert Stack as Superintendent (voice)

Ken Swofford as Coach (voice)

Francesca Marie Smith as Ashley B / Swinger Girl / Upsidedown Girl (voice)

Erik von Detten as Captain Brad Lawson (voice)

Paul Willson as Coach Kloogie / Mr. Detweiler (voice)

Patrick Renna as Jordan (voice)

Anndi McAfee as Ashley A (voice)

Lane Toran as King Bob (voice)

Rachel Crane as Ashley Q (voice)

Klee Bragger as Digger Sam (voice)

R. Lee Ermey as Colonel O'Malley (voice)

Clyde Kusatsu as Mr. Yamashiro (voice)

Clancy Brown as Bald Guy (voice)

Allyce Beasley as Miss Grotke (voice)

Gregg Berger as Tech #1 (voice)

E. G. Daily as Cap'n Sticky (voice)

Ron Glass as Dr. Lazenby / Tech #2 (voice)

Mark Robert Myers as Technician (voice)

Phil Proctor as Golfer #2 / Scientist #2 (voice)

Justin Shenkarow as Soldier Kid / Wrestler Kid (voice)

Michael Shulman as Hustler Kid (voice)

Katey Sagal as Mrs. Flo Spinelli (voice) (uncredited)