Steve Coogan as Campbell Babbitt

Hilary Duff as Lucy Diamond

Olivia Thirlby as Tess Sullivan

Josh Peck as Jim Lement

Molly Shannon as Penelope Little

Brett Kelly as Blastoff! Chorus

Molly Price as Donna Arbetter

Max Hoffman as Fenster Itski

Sarah Lind as Peggy Popoladopolous

Laura Carswell as Lute Lement

Ingrid Nilson as Ann

Andrea Brooks as Sue

Andrew Wheeler as Principal Person

Gabrielle Rose as Mrs. Bridigan

Colleen Rennison as Sylvia

Aubrey Mozino as Blyth

Alexia Fast as Hannah (uncredited)

Kendra Waldman as Dusty Drake

Aaron Brooks as Ezra

Barry Greene as Sam Calalluci

Levi Sochet as Sam Calalluci (voice)

Katie Messina as Gina

Alana Husband as Angela

Barbara Greenbaum as Librarian

Brenna O'Brien as Diminutive Girl

Aiden Lane Robson as Gustave Person

David Allan Pearson as Grease Monkey

Jilena Cori as Mrs. Person

Patricia Drake as Mrs. Itski

Ashley Whillans as Blastoff! Chorus

Calum Worthy as Blastoff! Chorus

Advah Soudack as Blastoff! Chorus

Robin Eder-Warren as Blastoff! Chorus