Tart of tongue and sweet of disposition, Juno offers living proof that crisp writing, graceful directing and an abundantly poised young lead can perk up a premise that’s been bludgeoned to death. Written by the alarmingly named Diablo Cody (real name: Brook Busey-Hunt; Diablo sounds like one of the names she took, including Bonbon and Cherish, in her previous career as a stripper) and directed with cheek and soul by Jason Reitman (Thank You for Smoking), the comedy spans nine weird months in the life of Juno MacGuff, a truculent working-class teenager played by 20-year-old Canadian actress Ellen Page, who on a tedious Midwestern afternoon gets herself knocked up by her dorky friend Bleeker (Michael Cera, suitably limp). On hand to up the usual ante are the boilerplate figures of the preggers-teen subgenre: Juno’s matter-of-fact, supportive father (J.K. Simmons) and tough-talking stepmother (Allison Janney); a kooky best friend (Olivia Thirlby), always ready at the other end of a hamburger telephone to help Juno find the perfect adoptive couple; and Mark and Vanessa (Jason Bateman and a very good Jennifer Garner), a brace of infertile Whole Foods yuppies who seem more than eager to give the forthcoming tyke a secure home.

But Juno doesn’t so much defy type as dance around it and set it free. Swathed in sexless flannel shirts and a carelessly pulled-back pony tail, our heroine appears at first an all-too-familiar figure, the marginalized teen-bitch ready to heap scorn on all things bourgeois or boring. Juno may be named for Jupiter’s wife, the statuesque Greek goddess of childbirth (and, not incidentally, revenge), but she’s much more lost in the forest than her snooty nonchalance suggests. Reitman’s autumnal palette and periodic forays into animation slyly nudge our attention in the direction of the little red hoodie Juno wears over her otherwise drab gear, a more accurate gauge of her emotional temperature than her big mouth. Careless of her beauty, Page, who previously turned heads playing a precocious 14-year-old who turns the tables on an apparent predator in Hard Candy, makes tiny adjustments to her delicate features that flag the fright and insecurity simmering beneath Juno’s bravado.

Like Amy Heckerling in her Fast Times at Ridgemont High and Clueless heyday, Cody has a sharp and sympathetic ear for the disclaiming argot of marginalized adolescents bent on claiming superiority to everything they fear. For all Juno’s coolly clinical appreciation of the “pork swords” jiggling in the shorts of jogging schoolboys, she has no idea what to do with the consequences of her fateful encounter with one of them. And so, all unawares, she makes a beeline for another, bonding with Mark over what she takes to be their shared love of guitar in a den that looks suspiciously like a playroom, while Vanessa adjusts her dimples downstairs.

Cody, whose clearly self-written bio in the production notes proffers the unsolicited news that she “never went to Harvard,” makes no bones about her class resentment: Vanessa’s misty-eyed dream of open adoption is rudely ?interrupted by Juno, who wants hard cash. Yet nothing is overdone in this movie, and if no one escapes a little parodic poke in the ribs, everyone gets to spring a cunning little surprise on the formula. Just when you’re thinking the movie is beginning to stew in its own cleverness, the plot takes a twist for the serious and then the frankly feminist.

I’m not sure I’d call Juno ground-breaking — for that you’d need a pimply heroine who stays that way and still gets the guy — but what sets this engaging little movie above the pack of glib, brittle or sickly-sweet teen comedies is the clear eye it casts on the suburban American family, while stoutly defending that battered institution’s elastic ability to adapt.

JUNO | Directed by JASON REITMAN | Written by DIABLO CODY | Produced by LIANNE HALFON, JOHN MALKOVICH, MASON NOVICK, RUSSELL SMITH | Released by Fox Searchlight | At ArcLight, The Grove, The Landmark

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