A tough cop is given his most difficult assignment: masquerade as a a kindergarten teacher in order to find a drug dealer.
- Detective John Kimble (Tom Cruise) - A tough street cop who's forced to take an undercover assignment as a Kindergarten teacher. In the end, retires and becomes a full time teacher!
- Joyce Palmieri/Rachel Myatt Crisp (Amy Adams) - A teacher whom Kimble falls for but who is also Crisp's ex-wife. In the end, marries Kimble
- Detective Phoebe O'Hara (Vikki Lewis) - Kimble's partner who gets food poisoning, forcing him to cover for her on the assignment. She briefly poses as Kimble's sister, "Ursula Kimble". In the end, bid farwell to Kimble!
- Miss Schlowski (Whoopi Goldberg) - The school's strict principal. Though initially suspicious of Kimble, she eventually grows to respect him when he assaults Zach's universally-disliked abusive father. In the end,hires Kimble!
- Cullen Crisp (Dougray Scott) - the main antagonist and a vicious drug dealer who is searching for Joyce and especially Dominic, respectively his ex-wife and son. In the end, gets killed by Kimble!
- Eleanor Crisp (Pat Carrol) - the secondary antagonist and Crisp's overbearing mother. In the end, ???
- Dominic Palmieri/Cullen Crisp, Jr. (Logan Grove) - Joyce and Crisp's son who becomes close to Kimble. In the end, ???
- Captain Salazar (Jeff Bridges) - Kimble and O'Hara's boss, in the end, ???
- Danny (Crispin Freeman) - A criminal who gives Crisp information on his family but is later shot to be kept silent.
- Cindy (Tara Platt) - She witnesses Danny's killing and becomes a state witness, but she is killed by Eleanor.
- Henry Shoop (Paul Giamati) - O'Hara's fiancee, in the end, ???