Watching Dakota Fanning snort coke off a dirty bathroom floor is kind of like seeing a dog in a dinosaur costume or Snooki on the red carpet: it’s adorable, but extraordinarily unconvincing. Dakota’s edgy role as rocker Cherie Currie in “The Runaways” was supposed to be her coming-of-age role — in fact, in the very first scene, Currie gets her first period: it’s Dakota’s way of telling us she’s no longer the little girl from “Uptown Girls” and “War of the Worlds.”

But Dakota’s uneven performance only reminds you how young she is: as she tries on a corset, you sigh; when she seduces an older man, you grimace; and when she melodramatically collapses from an overdose, you simply want to tell her to stop trying so hard. Dakota manages to make an entire performance feel like karaoke — an amateur shamelessly screaming the lyrics of a professional, as if that will make her sound like Aretha Franklin.

Despite Dakota’s deficiencies, the film certainly has its moments, mostly thanks to Kristen Stewart’s unrecognizable turn as Joan Jett. Stewart commits to the role completely, without an ounce of vanity or pretention. Her performance makes the audience wish the film focused on Jett, rather than Currie’s Jenny Humphrey knockoff.

The movie is at its best, unsurprisingly, in the performance and rehearsal scenes, as The Runaways begin to come together as a band. Dakota’s standout moment (well, relatively speaking) is in the climatic rendition of “Cherry Bomb.” The rehearsal scenes — mostly thanks to Michael Shannon’s eccentric Kim Fowley — are fun to watch as well. They feel like Hollywood Week on “American Idol,” except if Simon were aggressive, flamboyant and threw dog shit at the contestants.

In the age of Lindsay Lohan, Ke$ha and Lady Gaga, the movie manages to be relevant and poignant, as it covers themes of fame and expectations of women. At times, however, director Floria Sigismondi handles the feminist themes too transparently. In the first 15 minutes alone, a guitar teacher says, “Girls don’t play electric guitars,” the song “It’s A Man’s, Man’s, Man’s World” accompanies a montage, and Jett is told she’s looking in the wrong section of the store before she states that she wants to wear what “he” is wearing.

Sigismondi wrote the screenplay, as well, which is generally excellent, albeit oddly paced. The band’s ascent to super stardom is portrayed only through a montage of newspaper clippings (the only time that device is used in the movie), and at the climax of the film, eight months are inexplicably skipped over. Yet, we spend inordinate time dealing with Currie’s daddy issues.

This decision, ultimately, speaks to the intent of the film: it’s an adaptation of Currie’s autobiography and is more of a biopic of Currie than a story of the band. The problem is that Currie is the least interesting part of the movie, as played by Fanning. When Fowley first spots Currie — harmlessly standing doe-eyed and awkward in the corner — and wants her in the band, he tells her he’s intrigued by “the look on your face that says you could kick the shit out of a truck driver.” Fowley must be confused though. Dakota couldn’t look like she might kick the shit out of a truck driver if you murdered her puppy in front of her. Perhaps, then, Fowley was referring to the faces of the audience, impatiently waiting for the camera to turn back to Stewart.