The story begins in 1987 with Jenna, whose relationship with her parents is just fine but doomed to deteriorate in the years to come. The flat-chested 13-year-old is addicted to fashion magazines, particular one called "Poise" (a glorified "People" publication perhaps akin to "Vogue"), which convinces her that substituting big boobs for her dorky braces will mean that real life begins at 30. Wishing makes it so for Jenna (now played by Jennifer Garner). With the help of some angel dust, she finds herself with a lithe body inhabiting lush digs her New York Ranger boyfriend, a complete stranger to her, appearing half naked while in a future scene he embarrasses her by performing a strip tease. She quickly finds out that she's an editor at the very "Poise" magazine and that her foul friend Lucy Wyman works in the same capacity in an office next door.

Her life really changes, however, when she discovers that her nerdy childhood friend, Matt Flamhaff (now played by Mark Ruffalo), has blossomed into a cool guy, slimmed-down body, and a creative job in photography. As she works on her career at "Poise," she is now distracted by thoughts of the new Matt, due to be married in a few weeks, but not to her. Why not? In her rise to publishing heaven, she has discarded her old pals together with all the innocent values that good little children are said to possess.

Movie-goers will see obvious parallels between "13 Going on 30" and films spotlighting similar fantasies. In Penny Marshall's "Big" (1988), Tom Hanks inhabits the role of a 12-year-old who grows suddenly into a man of 30, while Gary Nelson's "Freaky Friday" last year pulls a mother-and-daughter switcheroo. Brett Ratner's "Family Man" highlights the Nic Cage character as a yuppie with no emotional ties, wondering whether he'd have been better off staying in New Jersey with the love of his life in a smart, imaginative tale that is very much a part of this exploited subgenre.

Notwithstanding the well-paced plot and a good sound track particularly the use of Michael Jackson's "Thriller" to illustrate a show-stopping dance and Pat Benatar's prescient song "Love Is a Battlefield" which sums up what Jena has lost, Jennifer Garner, whose not particularly appealing looks belie her effervescent personality, is no Tom Hanks. In fact cannot compare in comic depth with Barbara Harris or Jodie Foster in Gary Nelson's original 1977 "Freaky Friday." Save for the dance scene which parallels Penny Marshall's "Big" view of a 30-year-old dancing on an elongated piano keyboard at FAO Schwartz, "13" is predictable, thanks in part to the presence of so many other features of this nature. We are told that Jena has spoken rarely to her parents since she made a splash at the magazine and that she snobbishly ignores her neighbors as she proves when a 13-year-old next door is stunned to be spoken to by Jena for the first time. The icy descent is insufficiently delineated, the show-steal belonging not to Ms. Garner's work but to the talented, laid-back performance of Mark Ruffalo.