In my middle school years, American Pie fever swept the hallways, kids giggling at their lockers about the raunchy movie they snuck into. Jason Biggs and posse ushered in a new call for teenage raunch-fests that made our older brothers’ John Hughes movies look like PBS specials. Teenage boys grew accustomed to seeing their hyper-sexualized peers at the movies. We were frat boys in the making.

Meanwhile, teenage girls received a more varied education. Beyond the typical will-he-won’t-he romantic comedies (She’s the Man, 10 Things I Hate about You), there were many complex portraits of females navigating puberty, friendships, and sexuality—from the sardonic (Mean Girls) to the unattainable (The Virgin Suicides). Juno was a 2007 sleeper hit, where Ellen Page surprised dopey Michael Cera with her choice to have her baby. Yet nothing in this trajectory, up through Easy A and The Perks of Being a Wallflower, prepared me for the boldness of 15-year-old Minnie in Diary of a Teenage Girl.

Once Minnie admits to her mom’s boyfriend she wants to sleep with him, they fall into an intensely sexual relationship. As newcomer Bel Powley plays her, Minnie can be young and naively romantic, but also shrewd and adept at knowing what feels right. With a soulful soundtrack and golden-hazed shots of seventies San Francisco, director Marielle Heller’s movie catches the sweet spot when Minnie discovers she likes sex. “This makes me officially an adult,” she reasons.

Heller’s movie doesn’t place judgment on Minnie or even the boyfriend, Monroe. Minnie may not understand their coupling at the start, but this story embraces her experimentation on her terms. Yes, Monroe’s advances discomfort the viewer—even with the distance of the seventies—but Alexander Skarsgård’s mustached lover is more single-minded than predatory, searching like Minnie for intimacy. How to explain away his affair with a 15-year-old girl? The movie doesn’t try to answer.

There’s little that Minnie’s parental figures are able to offer a teenage girl. Her mom, Charlotte (an enjoyable Kristen Wiig), declares herself a feminist, then urges her daughter to work harder at attracting boys. With her carefully manicured appearance, and a drink always in hand, Wiig suggests a well of deep insecurities, a nagging inability to mother that Charlotte tries to cover up. Minnie’s stepfather, played by Christopher Meloni, is a fastidious East Coaster out of place in his children’s lives.

Writing her own story, recorded as a diary on tape, Minnie develops a fascination with her newfound power, seeking forbidden fruit in unexpected places. In Heller’s impressive first movie, sex becomes an empowering entry into a heartbreaking adult world.