At Ocean Front High School in Los Angeles, it is the last day of school before summer vacation. The gym teacher, Freddy Shoop (Mark Harmon), could not care less about his job and is ready to vacation in Hawaii with his young girlfriend, Kim.
Students get called to the office by the Vice Principal, Phil Gills (Robin Thomas) whom are told to attend summer school. The original remedial English teacher (Carl Reiner) wins the lottery and immediately quits his job. Gills has no choice but to give the job of teaching summer school to Shoop. Gills implies that not taking the job could keep him from getting tenure. As a result, Shoop has little choice but to stay in California, and Kim goes off to Hawaii without him.
On the first day, Shoop meets Robin Bishop (Kirstie Alley), who is teaching next door. Shoop falls head over heels for her, but she is already dating Gills. Shoop's first day is a disaster. Most of the students ditch and one hulking student named Jerome (Duane Davis) "goes to the lavatory" and is never seen again along with most of the others who ditch. Yet, a small group stays behind whom include: the day-dreaming and easily distracted Pam (Courtney Thorne-Smith); "nocturnal" Larry, who happens to be a male stripper (Ken Olandt); football jock Kevin (Patrick Labyorteaux)' pregnant Rhonda (Shawnee Smith); geeky Alan (Richard Steven Horvitz), whose older siblings are all straight-A students ("There must have been a baby mix-up at the hospital"); dyslexic Denise (Kelly Jo Minter) and two horror-film-obsessed underachievers, Dave (Gary Riley) and Francis, a.k.a. 'Chainsaw' (Dean Cameron) whom all are required to take remedial English.
That same day, Gills brings in a beautiful Italian transfer student, Anna-Maria (Fabiana Udenio), who will be learning English as well, much to the delight of Dave and Chainsaw. After the leftover students attempt to ditch as well, Shoop admits he has no idea how to teach. They spend their first few days having fun and going to the beach, a theme park and the petting zoo until Gills finds out.
Gills threatens to fire Shoop unless his students pass the end-of-term test. Shoop promises each kid a favor if they study. The kids agree, so Shoop agrees to give Denise driving lessons as well as help with her dyslexia; he accompanies Rhonda to Lamaze classes; he gives Kevin football lessons; he allows Dave to throw a party in his house (destroying his couch in the process); he gives Larry a bed in the classroom; he lets Chainsaw arrange a screening of the original 'The Texas Chain Saw Massacre' in his class; and he allows Pam to move in with him for the summer since she is neglected at home.
However, the laid back Shoop has no idea how to teach. Robin tells him to make teaching fun. Over the next few weeks, Shoop begins to grow closer to his kids. They study hard to write their English basic skills exam, they are still worried that Gills is going to fire Shoop unless all his students pass.
One day, Shoop is arrested and sent to jail when he covers for Chainsaw and Dave after they are found in possession of alcohol while hanging around the beach. Robin and Gills bail him out. At his court hearing, a sympathic judge, seeing that Shoop was willing to go to jail for his students, drops all the charges against him. Afterwords, Gills then inadvertently exposes his true self to Robin when he states that he cares nothing for Shoop or his students and she overhears him. She storms off angrily.
A few days later, Larry is fired from his stripper job when he is found out first by his aunt (who kisses him... with tongue) and then by his mother (after she puts five dollars in his g-string) whom apparently attended one of his shows. The students make more demands on Shoop and he quits his job in anger. He is then convinced to come back when his students start feeling guilty about what they did and they scare off Shoop's replacement with a series of stunts eerily reminiscent of 'The Texas Chain Saw Massacre' thanks to the makeup and prostetic gore effects that Chainsaw and Dave throw to show themselves off.
Shoop and his students then begin preparing for the test in earnest. Finally, the day arrives, and Shoop is suprised when Jerome, the student who "went to the lavatory" six weeks earlier, finally returns to the class to take the test, with his only explanation being, "My zipper got stuck." He ends up getting the highest score in the class with a 91%.
The exam goes smoothly despite Rhonda going into labor near the end (at least now she has grounds for a makeup). Not all pass, so Gills is ready to follow through with his firing threat. However, the parents of the students come to Shoop's defense when they arrive at the school to protest to Gilles not to fire Shoop. Because of the students' great improvement, Principal Kelban (Francis X. McCarthy) grants Shoop tenure for his positive effect. Shoop and Robin end up happily together; a la 'From Here to Eternity', they kiss in the surf.