The considerable strength of The Diary of A Teenage Girl lies with its writer/director Marielle Heller and her wise choice to cast relatively unknown British theater actress Bel Powley in the lead role of 15-year-old Minnie Goetz. The film, based on Phoebe Gloeckner's graphic novel, takes place in San Francisco during 1976. Minnie lacks self esteem, hates her body, and fails to see how anyone could possibly love her. That attitude changes after she has sex for the first time with her mother's boyfriend Monroe (Alexander Skarsgard) after propositioning him while both were extremely intoxicated.

Minnie suddenly feels empowered by the experience. Believing she is in a real adult relationship, the teenager continues to have sexual encounters with Monroe. In an attempt to understand the changes in her life, Minnie decides to record a diary on cassettes which she hides in her room so nobody else can stumble upon them. She hopes these cassettes will help her see how she has evolved as an individual when she plays them back in ten years.

Heller chose Powley to portray Minnie after the actress blew her away with an audition tape. Although auditioning hundreds of other girls for this lead role, the writer/director kept coming back to Powley, so she decided to fly the actress to New York for a meeting with Skarsgard, who was already cast. 

Powley and Skarsgard performed several scenes from Heller's script for over four hours. This allowed the director to determine whether they clicked together or not. The result? Heller knew she had found her Minnie.

The only thing Minnie feels totally confident about is her artistic ability. She longs to be a professional cartoonist like her idol Aline Kominsky (voice of  Susannah Schulman), who crops up in cartoon form when Minnie requires guidance most. This a good thing because she doesn't have anyone real in her life to turn to if she is grappling with a problem. Her mother Charlotte (Kristen Wiig) is always either drunk, hung over, or high on cocaine. No wonder she’s oblivious to her daughter's improper relationship with Monroe, although it’s happening right under her nose!

Minnie doesn't relate to her stepfather Pascal (Christopher Meloni), who has a PhD in science and appears rather distant. Still, he is the only person who knows Minnie’s true worth and that she’s actually quite bright. Unfortunately, he’s seldom available to her or to younger sister Gretel (Abby Wait).

I appreciate the way Heller never judges Monroe and lets viewers decide what kind of person he is. In this key role, Skarsgard comes across -- as Heller observes -- “terrific at building deep nuanced stuff below the character's surface." Wiig provides a strong multi-layered performance as Charlotte, and Meloni is convincing as Pascal. 

Heller's use of cartoons by Sara Gunnarsdottir gives us a window into Minnie's brain and innermost thoughts and desires. While The Diary of A Teenage Girl is Heller's directorial debut, it certainly doesn't seem like a first feature. Her skilled direction and strong screenplay is likely a result of spending eight years successfully adapting the material for the stage before turning it into a full-length movie.  

Heller displays an incredibly strong grasp of Phoebe Gloeckner's characters. She succeeds in getting flawless performances from her cast members, especially Powley, who brings depth, maturity, humor, and honesty to Minnie. That’s why it’s easy for viewers to relate to the teenage girl she portrays.

(Released by Sony Pictures Classics and rated “R” for strong sexual content including dialogue, graphic nudity, drug use, language and drinking -- all involving teens.)