Lance Clayton (Robin Williams) is a single father and high school English teacher. He dreams of becoming a famous writer, but his previous novels have all been rejected by publishers. His 15-year-old son Kyle (Daryl Sabara) is a pornography-obsessed underachiever who despises and is annoyed by everyone, especially his father. Kyle is a student at the school where Lance teaches an unpopular poetry class. His only friend is Andrew, a fellow student who spends his evenings at the Claytons' house trying to avoid his alcoholic mother. Kyle's consistently poor academic performance and vile behavior gain the attention of the school principal (Geoff Pierson), who advises Lance that Kyle should transfer to a special-needs school. Lance is in a non-committal relationship with a younger teacher named Claire (Alexie Gilmore), who is spending time with a fellow teacher named Mike (Henry Simmons), whose writing class is more successful than Lance's. On nights when Claire cancels their dates and he is alone, Lance bonds with his elderly neighbor Bonnie (Mitzi McCall).
One night, after Kyle and Lance spend an evening with Claire, Lance discovers that Kyle has died in an autoerotic asphyxiation accident in his bedroom. To avoid embarrassing his son, he stages Kyle’s death as a suicide. He writes a suicide note on Kyle’s computer and hangs his son’s body in the closet. A classmate later obtains the suicide note from police records and publishes it in the school newspaper. The note strikes a chord with the students and faculty, and suddenly many students claim to have been friends with Kyle and are touched by how deep and intelligent he shows himself to be in his writings.
Enjoying the attention his writing is finally receiving, Lance decides to write and publish a phony journal that was supposedly written by his son before his death. Kyle becomes something of a postmortem cult phenomenon at the school, and soon Lance begins to receive the adoration that he has always desired. Andrew finds Kyle’s suicide note and journals as highly uncharacteristic based on Kyle's personality when he was alive, but Lance brushes him off when Andrew confronts him. The journal soon attracts the attention of book publishers and Lance lands a television appearance on a nationally broadcast talk show. The school principal then decides to rename the school library in Kyle’s honor.
At the library dedication, Lance finds that he can no longer live with his lie and confesses before the school. Lance is denounced by the students and faculty, including Claire. Lance nevertheless feels reborn and dives naked into the school's swimming pool. Andrew tells Lance he knew the truth all along, and that he enjoyed Lance's writing. The two of them happily watch a zombie movie with Bonnie.Robin Williams as Lance Clayton
Alexie Gilmore as Claire Reed
Daryl Sabara as Kyle Clayton
Evan Martin as Andrew
Geoff Pierson as Principal Wyatt Anderson
Henry Simmons as Mike Lane
Mitzi McCall as Bonnie
Jermaine Williams as Jason
Lorraine Nicholson as Heather
Morgan Murphy as Morgan
Toby Huss as Bert Green
Tom Kenny as Jerry Klein
Jill Talley as Make-Up Woman
Bruce Hornsby as himself
Krist Novoselic as Newspaper Vendor (cameo)
Bobcat Goldthwait as Limo Driver (uncredited)
The film was shot in Seattle, Washington, largely at the former F.A. McDonald School in Wallingford. Seattle resident and former Nirvana bassist Krist Novoselic has a wordless cameo while consoling Robin Williams' character at a newspaper stand (Goldthwait had previously opened for Nirvana). Bruce Hornsby appears as himself at the library dedication.
World's Greatest Dad received critical acclaim, holding an 89% "Certified Fresh" rating on Rotten Tomatoes, based on 116 reviews, with an average rating of 6.9/10, with the critical consensus: "World's Greatest Dad is a risky, deadpan, dark comedy that effectively explores the nature of posthumous cults of celebrity." The film also holds a score of 69 out of 100 on Metacritic, based on 24 critics, indicating "generally favorable reviews."
The film was a hit at the Sundance Film Festival, the website hailing it as a "lusciously perverse, and refreshingly original comedy that tackles love, loss, and our curious quest for infamy." It also commented on Robin Williams' performance as outstanding. Sandra L. Frey observed the film's portrayal of teen angst, and said that the film also reminds the audience that adults can offer strong angst of their own. Devin Faraci called the film "brilliant" and "genius." Paul Fischer named it as one of the best films of the year. Ben Lyons and Ben Mankiewicz both gave the film favorable reviews on At The Movies. Mankiewicz saluted Daryl Sabara's performance as exceptionally well done, commented on the film's "remarkably funny script," and overall considered it a "little gem." Roger Ebert of the Chicago Sun-Times gave World's Greatest Dad 3 out of 4 stars, but noticed that the material could have been even darker in its satire, and he questioned whether it was the director's intention.
The DVD was released on December 8, 2009 and featured an audio commentary track with the director, deleted scenes, outtakes, and a making of featurette.