Your adolescence was nothing like Mia’s (Katie Jarvis), the fifteen year old protagonist of “Fish Tank.” Though there is a small chance that you too, could have grown up in housing projects outside of Essex, England to a state-supported single mom; nevertheless, it takes more than a tough childhood to create a character as vivid as the one that structures Andrea Arnold’s new film. And it takes an actress whose onscreen grittiness is not so much an act as a response to an environment that’s very close to home.

The scope is humble — we follow Mia around her house as she yells at her mom and exchanges spitfire wit with her squirt of a little sister. She wanders the streets around her town, goes to an internet café, the junkyard, the grassy fields nearby. Immediately smitten with her boldness, we are always with her — maybe one of the reasons you may not realize that Mia is alone in this world. She’s probably too tough and too smart-mouthed to befriend any of the other girls she runs into —her default is confrontation. And maybe it should be — though in one instance she picks a fight with stripper-esque peers, giving one a black eye, in the next she finds herself surrounded a gang of boys with a Rottweiler in tow — we fear for her as they grab her by the arms and legs. It’s next to their trailer that she’s found a horse tied up, which she repeatedly tries to free.

Though in reality her environment is doggedly bleak and stagnant, the film makes the world look intense, bright almost. Despite the hoodies and sweatpants that make up the total of her wardrobe, the camera always makes us aware of how fiercely pretty this fierce young girl is — a fact not unnoticed by her mother’s new boyfriend. Connor (Michael Fassbender) shows up early in the film and immediately makes her mother, herself a gorgeous, though insecure, woman, much snappier, dismissive and jealous than usual. From the time we see him bandage her foot injury, we know she’s crushing, and we try not to trust the warm and charismatic guy who we fear will take advantage of this. Connor seems to be the best thing that’s ever happened to the family, and too good to keep the audience from suspecting darker tones. You still may not be sure how to judge him, even after the creepy cookie crumbles — one of many emotional ambiguities at the center of the film.

Although it doesn’t hurt that this new guy is straight out of a Calvin Klein ad, Mia’s muted attraction may stem from his supportiveness — he watches her dance routine with sensual looks of approval and words of encouragement—likely the first she’s ever heard in her household. Self-motivation and discipline, however, is not lacking; she breaks into an abandoned flat to practice her hip-hop moves, rehearsing relentlessly for a dance audition.

But Mia breaks into other places too, and she runs a lot, sometimes toward things, sometimes away, always brash, always daring. For a few moments, we may remember what it is to be youthfully reckless, vicariously navigating a world without internalized fear of authority, judgment, or the future.

This is equally a testament to talent as it is to the director’s techniques. Shot in narrative order, the actors were given script piece by piece as the film was made — as uncertain of their fates as we are. Being with Katie Jarvis is a viscerally raw experience — her first time acting, she was cast when the Arnold saw her at a train station, yelling at her boyfriend across the tracks. If at times the style reminds you of documentary, it’s a homage to the grimy reality we’ve encountered with her. One too many coming-of-age stories reek of sentimentality, a sugar-coated whiff, notably and commendably absent in “Fish Tank.”