Anna Paquin stars as troubled teenager Lisa Cohen in writer-director Kenneth Lonergan’s “Margaret.”

The teacher holds his head in his hands. Lisa Cohen, a 17-year-old New York private school student, has cheated on her math test. With crossed legs and folded arms, she nasally claims that it’s not like she would “ever have to use math ever again.” Six hours later, Cohen is cradling the bloody, mangled body of a middle-aged woman in her hands, her snotty persona shattered by the woman’s desperate cries to talk to her daughter in her last moments.

With such a visceral opening gambit to catalyze its story and an able cast, “Margaret” could have proved a masterful coming-of-age film. The performers—Anna Paquin as Lisa Cohen, Matt Damon as her math teacher, Allison Janney as the accident victim, and Mark Ruffalo as the responsible bus driver—play each of their characters with a distinctly human touch. And even though Paquin’s Cohen is not likeable in the least, the actress perfectly animates her role as the daughter of a flaky actress who has been raised in privilege. However, despite these initial advantages, the film falls apart due to noisy editing and an even louder screenplay that together make “Margaret” a plodding, unrelatable mess whose best moments are over after the first promise-filled 15 minutes.

The set-up of “Margaret” is simple and effective. Cohen chases after a moving bus in an attempt to ask the driver where he got his cowboy hat. The driver, thoroughly distracted by Cohen’s waving arms and shouts, runs through a red light and into Monica Patterson (Janney), who spends the next 10 minutes in Cohen’s arms slowly dying from blood loss. Cohen’s crushing guilt for the accident causes her to slowly unravel as she hallucinates “Black Swan” style, complete with blood pouring from imaginary spigots and Patterson haunting her dreams. However, the film seems determined to ignore this main plotline in favor of around 10 other side plots that just serve to make both Cohen and the film similarly unappealing.

In the two and a half hours of “Margaret,” Cohen manages to scream at her mother once every 15 minutes; have three awkward phone calls with her father; lose her virginity to ne’er-do-well Paul (Kieren Culkin); seduce her math teacher; smoke marijuana; get into several heated debates about the right of Palestine to exist; listen to “King Lear;” and go to the opera. On top of all of these extracurricular activities, back in the main storyline Cohen also manages to organize a legal battle against the bus driver, attend Patterson’s funeral, call her family, visit the bus driver, and bond with the best friend of Patterson before screaming at her too.

The sheer busyness of “Margaret” would imply that the film is fast-paced and exciting, stuffed with every single possible element of a contemporary Bildungsroman. However, the construction of each one of these scenes makes each event seem highly annoying or simply boring. When Cohen leaves her math teacher’s house after coercing him to have sex with her, she whines, “Get over it. It was just sex,” before slamming the door. During class time, when Cohen engages in political debates, statements such as “[Arabs] killed 3,000 of our people” just sound like a lazy writer’s way of saying that Cohen is ignorant and looking for someone to blame.

“Margaret” would work as a series of short films, each designed to create a sense of malaise and anguish. However, when these moments are strung together, they become a torturous experience. Lisa Cohen, whose character could have been a great example of disaffected youth, instead becomes a sort of cut-out doll that writer-director Kenneth Lonergan shamefully uses to connect a slew of unrelated concepts that aren’t even novel.There’s little we haven’t seen before, from the teacher who can’t resist his student, to the mother who is too self-absorbed and the father who is distant and distracted, to the girl who can’t deal when real life runs her over.

In the end, by taking this string of character clichés and compounding their painful presence in the film through constant languorous slow-motion cityscape shots and unnecessary opera arias, Lonergan makes “Margaret” a parody of its own genre: an exaggerated portrait of adolescent angst so overwrought as to border on the comical.

—Staff writer Christine A. Hurd can be reached at churd@college.harvard.edu.