Juno is a small, quirky teenage comedy that was all set to become a cult classic like Rushmore – then went and charmed the world. It has ended up with four Academy Award nominations and $100m at the box office, and rising.

Considering its unconventional creative parentage, this cross-over success is remarkable. It was written by a newcomer, Diablo Cody (real name Brook Busey-Hunt), a former stripper with a degree in media studies, and directed by Jason Reitman, who did the funny libertarian comedy Thank You for Smoking.

The film is set in the suburbs of Minnesota, where 16-year-old Juno (Ellen Page) lives with her loving dad, Mac (JK Simmons), and stepmother, Bren (Allison Janney). When she learns that she’s pregnant, Juno decides, after an aborted visit to an abortion clinic, to have the baby, then give it to a childless yuppie couple, Vanessa (Jennifer Garner) and her husband, Mark (Jason Bateman).

It takes a little time to adjust to the film’s conspicuous quirkiness and clever dialogue. Inside a drugstore, Juno is subjected to such dialogue as “What’s the prognosis, fertile myrtle?” and “Your egg-o is prego” – and that’s just from the man behind the counter. One of the criticisms levelled at Juno is that everyone seems to talk like this. That’s not accurate. But there are enough funny lines, especially from Juno herself, to give that impression. One of my favourites is when she calls her girlfriend Leah (Olivia Thirlby) on the phone to tell her she’s pregnant. “Juno?” Leah asks. “No,” Juno says, “it’s Morgan Freeman.”

For all its sparky wit and indie-soundtrack sweetness, Juno is a serious and acutely observed study of a knowing yet naive girl trying to establish relationships, with peers and adults, in a world where relationship rules and roles are in a state of flux. The father of Juno’s child is Paulie Bleeker (Michael Cera), a sweet, skinny jock with a squeaky voice who is full of geeky charm. One of the best scenes in the film is when Juno tells Paulie she is pregnant. What we see is two scared teenagers trapped in prescribed responses. She hides her longing for him to say “Let’s have the baby” beneath cool flippancy. He hides his longing for her by going along with whatever she wants, and ends up appearing indifferent.

Page gives a remarkable performance as Juno. Physically, she is perfect for the role. The 20-year-old Canadian actress actually looks 16. And she gets this sadness around the eyes that quietly signals the aching heart lurking beneath her hip teenage bravado. For all her sophistication, she’s still a young and confused girl. When she first tells her dad she is pregnant, he says: “I thought you were the kind of girl who knew when to say when.” Obviously hurt, she looks at him and says: “I don’t know what sort of girl I am.” It’s a poignant, lump-in-throat moment. For all its hip coating, Juno is never too cool and clever to show its heart.

12A, 96 mins

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010