Thorton Melon is a prosperous businessman, renowned for his nationwide chain of clothing stores catering to plus-sized individuals. Despite his towering achievements, Thorton, portrayed by Rodney Dangerfield, comes from a modest background. His father continuously urged him to excel academically, yet Thorton never set foot in college. During a meeting with his executive team, he embraces fresh investment opportunities while contemplating tweaks to existing ventures. It's then his son, Jason, a student at Grand Lakes University, reaches out. Thorton inquires about Jason’s college life, asking how he’s faring with his studies, fraternity, and the diving team. Jason claims everything is splendid but conceals the truth—he doesn’t participate in a fraternity and is only the diving team’s towel boy.
At a swanky dinner gathering hosted by his snobbish and extravagant second wife, Vanessa, Thorton remarks that the attendees are merely after free food and donations. While rummaging through the fridge for a beer, he discovers Vanessa in a compromising position with another man, Giorgio. Although he has been aware of the affair for quite some time, Vanessa's demand for a divorce prompts Thorton to present her with legal papers and shocking evidence in the form of Polaroid photos of her rendezvous.
After the event, while practicing diving in his lavish pool, Thorton confides in his aide and bodyguard, Lou, expressing regret that Vanessa has tainted his relationship with Jason. Determined to mend their bond, he surprises Jason with a visit to Grand Lakes. However, Thorton mistakenly arrives at a sorority house, only to find out Jason isn’t in a fraternity nor is he part of the diving team. Jason confesses to feeling isolated and unsuccessful at college, leading Thorton to urge him to persist with his education and ultimately decide to enroll as a freshman himself.
Without any prior academic credentials to justify his admission, Thorton cleverly convinces the academic dean, Dean Martin, to allow him in by pledging donations for a new business school building in his name, thus establishing the Thorton Melon School of Business. The dean of the business department, Philip Barbay, is appalled by Thorton’s bribe, yet Thorton counters with his extensive real-world business experience, which he believes outweighs Barbay's theoretical knowledge.
Once enrolled, both Thorton and Jason take Barbay’s class, where Thorton debunks nearly every point the professor raises during discussions centered around building fictional companies. Their college journey continues as they attend a literature class taught by Diane Turner, where Thorton finds himself smitten. Despite Diana’s commitment to Barbay, she is drawn to Thorton’s carefree demeanor, leading to a romantic connection. Meanwhile, Jason attempts to forge a bond with Valerie, a girl he admires, though she is entangled with the self-important student, Chas.
In a wild twist of events, Thorton comes to the rescue of Jason's politically inclined roommate, Derek, during an altercation with the football team, ultimately igniting a rollicking brawl. Thorton’s college experience expands as he reconnects with the diving coach who once saw him dive professionally in Atlantic City, learning that Jason had attempted and faltered during a dive audition. Instigated, Thorton urges Jason to showcase his talent before the coach by executing a challenging dive.
While navigating the festivities of college life, Thorton enjoys the advantages of youth, reveling in parties and interactions with fellow students but struggles with the academic workload. In an attempt to alleviate his burdens, he hatches a scheme involving hiring experts to handle his assignments, infuriating Jason, who is eager to complete his projects independently. The tension escalates when Jason secures a spot on the diving team, leading to further disappointment as Jason suspects Thorton of leveraging influence for his son's advantage.
Amidst a boisterous party in the opulent dorm Thorton revamped, Diane catches him in a compromising situation with several young women. Her approval wanes when she reviews a literature paper he submitted, belittling his understanding of author Kurt Vonnegut. Subsequently, Barbay files accusations of academic impropriety against Thorton, who insists on his honesty but faces Barbay's counterclaims that he should take his finals orally to prevent cheating.
Exhausted and pushed to the limit, Thorton contemplates walking away. Yet, spurred by Jason's encouragement, Derek, and Lou stepping in to help him cram, he decides to confront his exams. On the day of reckoning, Barbay presents Thorton with a grueling question consisting of 27 parts. Through sheer determination, Thorton navigates the session, and with a nudge from Diane referencing Dylan Thomas’ poem, he finds the strength to press on and ultimately succeed.
In an exciting twist, on the same day as the Grand Lakes diving team's match, Jason shines in the competition. However, they start to lag behind in scores, prompting the diving coach to call on Thorton to perform his legendary Triple Lindy dive, reminiscent of his younger days. With a little persuasion from Lou, Thorton showcases his skills, dramatically turning the tide in the match. Following the victory, Diane pleasantly surprises him with his exam results - a mix of D's and one A from her class.
Finally, Thorton is invited to address the graduating class with humor-filled wisdom, where he encourages them to embrace their college journey and strive for success, leaving the audience in stitches.
