When her prep school eliminates girls' soccer, star player Viola Hastings (Amanda Bynes) switches teams all the way. Putting shared custody to work for her, she takes the place of her twin brother Sebastian (James Kirk) at his new school, their old school's rival, while he absconds to London with his band. Mom (Julie Hagerty), meanwhile, is too absorbed in the upcoming deb ball to notice, and Dad is out to lunch with his collar turned up. Obviously, conditions couldn't be more perfect for a girl looking to pass as a boy to trounce her ex-boyfriend on the pitch, which is just what she does.

She gets away with it thanks to her stylish hairdresser friend and some coaching in male swagger. As a boy, the doe-eyed, baby-faced Bynes makes a pretty convincing weirdo, and it's a wonder she doesn't ever find herself staring down the barrel of a Kolar during the movie. But her roommate, Duke (Channing Tatum), is not only the soccer team captain, he's also a sensitive guy, and open to ideas. When Viola-as-Sebastian claims the tampons in her luggage are for nosebleeds, he manfully gives them a try.

A breezy farce adapted from Shakespeare's "Twelfth Night" by first-time screenwriter Ewan Leslie and Karen McCullah and Kirsten Smith ("10 Things I Hate About You" and "Legally Blonde"), "She's the Man" is so good-natured, and its cast seems to enjoy itself so thoroughly, that the total annihilation of disbelief it requires winds up feeling like a reasonable enough request.

Bynes' loony boy shtick is completely unbelievable and thoroughly entertaining. But it's the crush she develops on Duke, who has a crush on Olivia (Laura Ramsey), who has a thing for Sebastian, that brings the movie to life. Furtively mooning over her hunky roommate, Bynes captures adolescent puppy love in all its loopy glory, and it's unexpectedly refreshing to watch a clever girl pursue the dreamy object of her desire.

Surrendering to silliness proves to be a good move; the movie stars David Cross as — what else?— the school's and clueless headmaster, and as the ditzy mom, Hagerty is as breathless and spaced out as ever.

"She's the Man" doesn't attempt to redefine the genre, in the manner of, say, "Ferris Bueller's Day Off." Much of what ends up on-screen feels familiar — the social pariah girl with a retainer echoes a long-ago Joan Cusack; the excellently choreographed soccer sequences recall "Bend It Like Beckham," but there's a sweetness about it that wins you over.