"13 Going on 30" is Garner's first major leading role as Jenna Rink, a 30-year-old fashion magazine editor in New York City. However, she doesn't feel 30 at all - when she was 13, she made a wish to be 30 (all it took was some sprinkling wishing dust). And presto, she is 30! She has bigger breasts, no braces, a handsome boyfriend (some hockey player), a bitchy co-worker, a fast-talking, goateed boss, a nice apartment, an autograph by Madonna, and a limo service to go to any party. She seems to have it all until she realizes she had sold ideas to a rival magazine, had ignored her parents and, even worse, ignored her best friend Matt since high school. The grown-up Matt (Mark Ruffalo) is a photographer who is confused by Jenna's need to be friends with him again. Meanwhile, Jenna shows she is caring and can dance a storm, especially to Michael Jackson's "Thriller."

"13 Going on 30" is sort of the female version of Tom Hanks' "Big," but the difference is she switches bodies in her mind (unless that wishing dust can really work miracles. It is never made clear). The humor quotient is derived from the adult Jenna's lack of memory of what happened to her since she was 13. But what makes the movie irresistible is Garner's convincing notion of a 13-year-old girl inside a 30-year-old body. She plays it to the hilt, calling grown men "gross," getting a group of 13-year-olds together to talk about love, confused by the ringing of cell phones, responding with a chuckle to being called a bitch and having to repeat it, looking away with disgust at hairy bare-chested men, and so on. Garner is so damn convincing that she makes the movie worthwhile since she occupies almost every single scene.

But there are screenwriting fallacies that may make you wince (you'll remember them after you are finished laughing). For one, doesn't anyone in the entire movie ever realize she acts and talks like a 13-year-old girl? Not even her parents. Not one at the office especially. And what seems like a cringe-inducing sequence where Jenna delivers the new look for the magazine (something to do with photo collages) is not given the proper payoff. Or let me just say that the editor-in-chief should've known better than to react the way he does.

The star of the movie is clearly Jennifer Garner and, flaws aside, she makes the movie her own. She also has a nice rapport with Mark Ruffalo in what may be his most sincere performance yet. "13 Going on 30" will make you laugh and for audiences nowadays, that may be enough.