RATING |

If it does nothing else, 17 Again - in which a tired, middle-aged Matthew Perry revisits his robust teenage self (Zac Efron) and finds it's a wonderful life - proves the durability of the body-swap fantasy.

But 17 Again also showcases the previously unseen acting talents of Efron, the Tigerbeat cover boy best known as the shaggy haircut of the High School Musical series and the pompadour of Hairspray. (His latest coif combines comb-over with the bowl cut, which produces the effect of a freaky friar.)

Much to my surprise, in 17 Again I wasn't conscious of watching Efron at all. I was watching a 37-year-old in the body of a 17-year-old, a father of teenagers flabbergasted at how his kids were acting in school and at how much senior high had changed in 20 years.

While the movie - a little Big, a little Back to the Future, a lot 13 Going on 30 - feels shelf-worn, Efron's performance is fresh. (His quizzical face and unfamiliar body remind me of Steve Martin's performance in All of Me, in which crotchety heiress Lily Tomlin inhabits the body of public-interest lawyer Martin.)

The film opens in 1988, when Mike O'Donnell (Efron), a high school hoops star hoping to be scouted at the Big Game, chooses love over basketball.

Fast-forward 20 years and Mike is now paunchy, Grinchy Matthew Perry, whose life did not work out the way he planned. He is on the brink of a divorce from his high school sweetheart, Scarlet (Leslie Mann), when he falls into a wrinkle in time and reverts to his 17-year-old self, but in 2008 and with the consciousness of a 37-year-old.

Unevenly directed by Burr Steers, who made the fascinating teen dramedy Igby Goes Down, this overlit and underwritten film gets many of its laughs from age-inappropriate encounters. As when the teenage Mike acts like a father to his teenage kids (Michelle Trachtenberg and Sterling Knight). As when the strapping, youthful Mike fawns over Scarlet, who can't understand why she is so attracted to a boy her son's age.

This leads to one of the film's squirmworthy moments, when Mike's daughter comes on to the teenage Mike, which in Jason Filardi's rough script is decidedly not handled with the grace of the comparable scene in Back to the Future.

Though the film rests on the enviably sculpted shoulders of the spirited Efron, Thomas Lennon and Melora Hardin provide some comic relief as Mike's nerdy friend and the fetching high school principal on whom he nurses a crush. For me, 17 Again is mildly diverting. For the tweens who are its target audience, Efron's outside shot is a three-pointer.

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Contact movie critic Carrie Rickey at 215-854-5402 or crickey@phillynews.com. Read her blog, Flickgrrl, at http://www.philly.com/philly/blogs/flickgrrl/.