Kindergarten Cop is a 1990 American comedy thriller film by Ivan Reitman and starring Arnold Schwarzenegger.
After years of pursuing drug dealer Cullen Crisp, Los Angeles Police Detective John Kimble (Schwarzenegger) has him on a murder charge after Crisp shot and killed an informant who had given him information regarding the whereabouts of his ex-wife, Rachel Myatt Crisp, and his son Cullen Jr. However, the only witness, a drug-addicted girl named Cindy whom the informant had brought to the meeting, is deemed too unreliable to put Crisp up for a permanent prison charge, so Rachel Myatt has to be found and persuaded to testify.
Kimble, accompanied by Detective Phoebe O'Hara, a former teacher, go undercover in Astoria,Oregon, to find Crisp's ex-wife Rachel. It is believed that Rachel stole millions of dollars from Crisp before fleeing. The detectives plan to offer her a deal to testify against Cullen in exchange for immunity. O'Hara is to act as the substitute teacher in the son's Kindergarten class at Astoria Elementary School, while Kimble is to discover the identity of the mother.
Unfortunately, O'Hara, who is hypoglycemic, falls ill with a terrible case of stomach flu at the last moment, so Kimble takes the teacher's job. The school principal, Miss Schlowski, is suspicious, but Kimble adapts progressively to his new status even though he has no formal teaching experience. Using his pet ferret as a class mascot, his police training as a model for structure of the classes, and positive reinforcement, he becomes a much-admired and cherished figure to the children. In turn, Kimble begins to love his cover job and his young charges, to the point where he severely deals with a case of child abbuse by assaulting the abusive father, finally winning Miss Schlowski's favor.
One of Kimble's students is a boy named Dominic. Kimble becomes fond of Dominic's mother, Joyce Palmieri, who also works at the school. Joyce, like many other of the students' mothers, is estranged from her husband, so that she will not speak of him. This excites Kimble's suspicions. In a series of conversations with the gradually more trusting Joyce, Kimble slowly deduces that she has to be Rachel Crisp and that Dominic is Crisp's son.
Meanwhile, back in California, Cindy dies after using spiked cocaine provided by Crisp's mother, Eleanor Crisp. The case is dismissed because the prosecution has no other evidence. Crisp is freed from prison and immediately heads to Astoria, where he and his mother immediately begin looking for the child. Crisp starts a fire in the school in order to get the boy but he is seen. Crisp takes his own son hostage, but Kimble manages to kill him after Crisp is bitten by Kimble's pet ferret before he can hurt Dominic. Crisp's mother then discovers her dead son, but before she can shoot Kimble, O'Hara arrives and knocks her unconscious.
Crisp's mother is arrested, while the unconscious Kimble (much to the sadness of the children) is hospitalized. During Kimble's recovery, O'Hara and her chef fiancée announce their marriage, inviting him to the wedding. After Kimble recovers, he quits the police force and returns to the school. The kids are very happy to see him, and Joyce comes into the classroom and kisses him in front of all the kids.