Like the titular character's accidental pregnancy, Juno has a fumbling start and an affecting delivery. With a plot that promises plenty of the twee, phony "edginess" that makes big-time studios open their wallets for little-movies-that-could, Jason Reitman's surprise festival-favorite at first warrants such fears with a cutesy opening in which 16-year-old Juno MacGuff (Ellen Page) learns of the consequences of her one-time fling with fellow high-school outcast Paulie (Michael Cera). When the sardonic heroine goes for a third pregnancy test at a convenience store and trades overwritten sitcomisms (inevitably laced with pop-culture references) with the clerk (a dependably dry Rainn Wilson), the movie seems primed for a reprise of the pesky glibness of the director's previous Thank You for Smoking. Surprise is what redeems the film's archness: Just when one is about to write off Diablo Cody's much-praised screenplay as less than the sum of its ornate quips, a scene will be flipped in an unexpected direction and a hidden vein of emotion suddenly struck.

Like Knocked Up, Juno tiptoes cautiously around the unwanted pregnancy at its center, though its underage protagonist does pay a visit to what the earlier film dubbed the "shmashmortion clinic." Juno decides to go through with the pregnancy but give the baby up for adoption to a childless yuppie couple, Mark (Jason Bateman) and Vanessa (Jennifer Garner). As she balloons into a "cautionary whale," she ping-pongs between Paulie and Mark, pretending that her night together with the former was the result of boredom rather than love while seeing the latter as a cool older brother (even if he prefers Hershell Gordon Lewis over Dario Argento). When she learns of the cracks beneath the couple's seemingly happy veneer, the character's adolescent attitudinizing is chipped and her sarcasm is finally exposed as a protective scrim from her fear of adult responsibility. Post-Ghost World, the caustic nerdette with a soft heart can be a cliché, but Page plays Juno with a forthright spikiness that never rounds off her edges.

Tart and plaintive, Juno is a welcome alternative to Judd Apatow's boys-only comic treehouses. If it isn't nearly as funny as either Knocked Up or Superbad, its poignancy nevertheless feels earned rather than shoved in. There's a refreshing absence of adversarial divisiveness between the movie's teenagers and adults: The genuinely affectionate support Juno's parents (J.K. Simmons and Allison Janney, both graciously subdued) lend their daughter is a lovely example of how Reitman and Cody subvert teen-comedy expectations, while Mark's growing attachment to the pregnant teen—equal parts mildly predatory infatuation and melancholy yearning for lost youth—is handled with dramatic heft. No less vitally, the picture delves deftly into the girl's desire, a side habitually taken for granted in portrayals of teenage relationships but here celebrated in such bits as the offhand, almost lyrical way a young receptionist at the abortion clinic recommends a condom that "makes my boyfriend's junk smell like pie." Taking its tone from the heroine, the film at times strives too hard for wise-beyond-its-years coolness, but, in moments like Juno's tender gaze as Vanessa feels the baby kicking inside her belly, strikes a delicate balance between snark and vulnerability.