Evan Rachel Wood’s performance in “Thirteen” is far better than “Thirteen” is. She plays a middle school student named Tracy who is in the painful stage between childhood and adolescence, just learning how to be a woman and doing it all wrong, particularly due to having the wrong person mentoring her. Wood, who is 14, is absolutely fearless in her portrayal of pubescent angst, piercing the film with emotion that is absolutely convincing.

The film, alas, is not as good. Directed by first-timer Catherine Harwicke, it casts about for solid footing and is unable to locate it. The setting is L.A., where society’s skewed view of how women ought to be is visible on every billboard and signpost, and that theme is examined very briefly as a factor of Tracy’s behavior. Much greater attention, however, is paid to Tracy’s friend Evie (Nikki Reed, who co-wrote the screenplay, incredibly), a rootless, amoral “bad girl” who soon has Tracy acting, thinking and dressing just like her. Sex, drugs and stealing are all part of Evie and Tracy’s lifestyle, as Tracy’s mother Melanie (Holly Hunter, playing yet another put-upon single mom) looks on in distress.

All of this is well and good, but what’s the point? If it’s a story about the dangerous influence of evil friends — “Tracy was playing with Barbies before Evie came along!” Melanie yells during a catfight royale with Evie’s useless foster parent — then why the overriding emphasis on Tracy’s emotions? The implication starts to be that Tracy would have gone this way anyway, or at least that this is fairly typical rite-of-passage stuff for young girls — in which case, what purpose does Evie serve in the movie at all? Characters who function only as catalysts don’t generally warrant this much screen time.

In the end, I suspect we’ve been given an accurate representation of the brattiness, rebellion and overwhelming emotion that comes with being a 13-year-old girl. The question is what we, or any of the characters, have learned about it. We’ve been through an ordeal — and one thrillingly acted by Wood — but why?

C (1 hr., 40 min.; R, a lot of harsh profanity, some nudity, some strong sexuality, some blood.)