You may wonder why it was necessary to add 17 Again to Hollywood’s long list of “body swap” comedies over the last 25 years, but I have a theory. At some point in the rise of every young would-be star, the movie industry needs to figure out if they’ve got what it takes. Fish-out-of-water premises – body swapping, time travel, cross-dressing – may be a dime a dozen, but when you plug in the hot up-and-comer du jour, it’s like the cinematic equivalent of a duplicate bridge tournament. When everyone’s playing the same cards, you can figure out who’s really got game.

The results over the years have been decidedly mixed. Michael J. Fox (Back to the Future), Tom Hanks (Big) and Lindsay Lohan (the 2003 Freaky Friday remake) scored hits. On the other hand, Charlie Schlatter cavorted as a teen George Burns in 1988’s 18 Again!, and basically disappeared into workmanlike obscurity. Now it’s High School Musical star Zac Efron’s turn. 17 Again sort of works – except that one wild card steals Efron’s thunder.

This variation opens in 1989, where high-school basketball stud Mike O’Donnell (Zac Efron) is looking at a college scholarship – except that he opts to do “the right thing” and marry his girlfriend Scarlett when she gets pregnant. Twenty years later, Mike (Matthew Perry) is a defeated pharmaceutical salesman, and Scarlett (Leslie Mann) is tired of feeling like the scapegoat for his failings. Facing divorce and unemployment, Mike encounters a mysterious janitor (Brian Doyle Murray) and suddenly finds himself transformed back to his 17-year-old self. It’s a chance to start his life over again.

Screenwriter Jason Filardi (Bringing Down the House) and director Burr Steers (Igby Goes Down) fill the story with all the requisite elements. There’s the one person who knows the truth – Mike’s nerd-turned-software millionaire best friend Ned (Reno 911!’s Thomas Lennon) – to act as our protagonist’s confidante. There’s a jerk adversary – bullying jock Stan (Hunter Parrish) – to provide external conflict. And there are plenty of moments for awkward reaction takes, so that we can discover if the star is more than a pretty face.

But Stan proves to be a pretty tepid adversary and Steers wastes the presence of the talented Mann. If they wanted a bland backdrop for Efron, the filmmakers mostly succeeded.

What they didn’t count on is Lennon. He’s hilarious as a one-time loser who has succeeded to the point where he can fill his house with nerd-arobilia like life-sized Darth Vaders and a landspeeder for a bed, but still has no idea how to get a date. A subplot involving Ned’s flailing attempts to woo the high school principal (The Office’s Melora Hardin) serve up nearly all of the film’s biggest laughs, and Lennon’s deadpan delivery steals absolutely every scene he’s in.

That’s a shame. Efron’s got more than a little bit of charm beyond his dreamboat looks. But it’s generally much harder to make the teen-playing-grownup side of this concept work than the reverse – where Hanks, Jamie Lee Curtis and Jennifer Garner (13 Going on 30), delivered charming performances. You need a bit of soul beyond your years to pull off the weary wisdom of a guy flipped from mid-life crisis to big man on campus. When Efron attempts a tearful monologue expressing Mike’s love for his wife, he just seems like a kid play-acting at understanding those emotions.

17 AGAIN (2 ½) Directed by Burr Stears. • Starring Zac Efron, Thomas Lennon, Leslie Mann. • PG-13, 102 min. • At Century Cinemas Del Monte Center, Maya Cinemas and Northridge Cinemas..