Steve Coogan
— Campbell Babbitt
Hilary Duff
— Lucy Diamond
Olivia Thirlby
— Tess Sullivan
Josh Peck
— Jim Lement
Molly Shannon
— Penelope Little
Brett Kelly
— Blastoff! Chorus
Molly Price
— Donna Arbetter
Max Hoffman
— Fenster Itski
Sarah Lind
— Peggy Popoladopolous
Laura Carswell
— Lute Lement
Ingrid Nilson
— Ann
Andrea Brooks
— Sue
Andrew Wheeler
— Principal Person
Gabrielle Rose
— Mrs. Bridigan
Colleen Rennison
— Sylvia
Aubrey Mozino
— Blyth
Alexia Fast
— Hannah (uncredited)
Kendra Waldman
— Dusty Drake
Aaron Brooks
— Ezra
Barry Greene
— Sam Calalluci
Levi Sochet
— Sam Calalluci (voice)
Katie Messina
— Gina
Alana Husband
— Angela
Barbara Greenbaum
— Librarian
Brenna O'Brien
— Diminutive Girl
Aiden Lane Robson
— Gustave Person
David Allan Pearson
— Grease Monkey
Jilena Cori
— Mrs. Person
Patricia Drake
— Mrs. Itski
Ashley Whillans
— Blastoff! Chorus