Tracy (Evan Rachel Wood), buzzed on a can of compressed air, is feeling no pain. Staring directly into the camera, she begs the person sitting across from her to slap her-hard. One slap leads to another. She demands to be punched. Pow! Down she goes, split lip and all.

Thus goes the amazing opening scene of Thirteen, Catherine Hardwicke’s in-your-face portrait of two out-of-control teenaged girls. Strong stuff, and, I hoped, a taste of what was to come. But as effective, even harrowing, as the film sometimes is, it suffers from a sketchy, underdeveloped script (co-written with Hardwicke by costar Nikki Reed and supposedly based on the then-13-year-old’s life) that is considerably less shocking than anything by Larry Clark (Kids, Bully).

Tracy lives in a single-parent home with her brother and mom, Mel (Holly Hunter). She is reasonably popular for a sixth-grader (though she looks at least 16), but not part of the A-list crowd. Why can’t she be cool and popular like sexy-beyond-her-years Evie (Reed)?

Apparently, all it takes to win over her self-promoting classmate is to steal someone’s wallet, go on a shopping spree and start dressing like a slut. Overnight the formerly snotty Evie becomes Tracy’s best friend, all but moving in with her family while introducing the fawning teen to the not-so-wonderful world of drugs, boys (all black, curiously — are we to perceive that as some sort of statement about racism?) and body piercings. I don’t doubt that many of the incidents depicted in the film actually happened to Reed, or that young girls exposed to intense peer pressure will do anything to fit in, including shunning authority figures, letting their school work slide and giving guys blowjobs. But just because something is true, or makes us uncomfortable, doesn’t mean it translates — to borrow a phrase — into good theater. Even well-meaning cautionary tales require a certain amount of character development (and logic), and that’s where Thirteen comes up short.

Despite her newfound R-rated behavior, Tracy isn’t that far removed from your average misunderstood teen from any number of After-School Specials. If her objective is to win over the Most Popular Girl in School (which she accomplishes), why does she continue to act out with such reckless abandon? (It’s got to be more than just having an absentee father.) Why does Mel, characterized as a caring, concerned, with-it mother, allow the scheming Evie to stay with them when it’s obvious she is corrupting, even destroying, her daughter?

Hardwicke, in her impressive directorial debut (she won the Director’s Award at Sundance this year), coaxes terrific performances from her cast, especially her three female leads (Hunter is especially good). Working with inventive cinematographer Elliot Davis (whose constant panning and zooming is a bit disorienting at times), Hardwicke skillfully shows us the mounting horrors that transform Tracy from honor student to self-destructive tart. But after a while, we start to disconnect from sheer overkill. Our reaction to the disturbing back-to-back good girl gone bad vignettes shifts from distress to outrage to sadness to emotional stupor — like a prizefighter dazed by one too many successive blows. Yeah, kids are wilder and more out of control than ever, and being a parent is often a tough, thankless job.

What else is new?

As intermittently powerful as Thirteen is as it examines Tracy’s fall from grace, it doesn’t move us any closer to understanding her (or any other 13-year-old girl, for that matter). That seems to me a huge failing in a movie that wants to bridge the communication gap between mothers and daughters.

Thirteen starts Sept. 5 at Landmark’s Hillcrest Cinemas. Phone (619) 299-2100 for more information.

Kyle Counts is the film critic for the Gay and Lesbian Times.