In his directing debut, Jonah Hill offers a loose, limber coming-of-age vignette about a Los Angeles kid who escapes his nasty home life by bonding with a pack of streetwise skateboarders. “Mid90s” is barely feature length, but it shows a lot of heart while avoiding afterschool special-type cliché.

Sunny Suljic, seen recently as the semi-villainous classmate in the misbegotten Jack Black vehicle “The House With a Clock in Its Walls,” is Stevie, whose single mom Dabney (Katherine Waterston) seems more interested in her own one-night stands than the fact that her teen son Ian (Lucas Hedges) is regularly brutalizing his little brother. Stevie takes off on his bike and is absorbed in the freewheeling antics of a bunch of older kids who hang out at the Motor Avenue Skate Shop.

They’re Ray (Na-kel Smith), the only black guy in the group, who has his eyes on a pro career; Fuckshit (Olan Prenatt), a wild man extrovert with a mane of shoulder-length blond hair and an engaging smile, but an extra-foul mouth and a habit of flying off the handle; Fourth Grade (Ryder McLaughlin), a sweet but rather dim fellow with a video camera at hand; and Ruben (Gio Galicia), the youngest of the lot, who acts tough but has an insecure streak. None of them, it seems, has any home support to speak of, and they congregate at the shop to mess around, either on their boards on the front sidewalk or in the back lot, or sitting around inside bantering with each other.

Stevie notices them while bicycling by and finds them irresistible. At first he pretends to be looking over the shirts they sell in the shop, but soon, desperate to join the camaraderie, dickers with Ian to get his old skateboard and shyly enters their orbit, with Ruben initially welcoming him like some sort of disciple. The kid’s overjoyed when given the simple task of filling a half-gallon milk bottle with water for the crew as they skate, and, after bargaining with Ruben to get a more acceptable board—to get the cash for which he joins Ian in stealing some of their mother’s stash—he practices endlessly, not minding the constant spills on the driveway even though he lies to his mom about the theft, putting the blame solely on Ian—which of course gets him another beating.

But that doesn’t matter, since he becomes more and more a part of the group; as the older guys, especially Ray, adopt a quasi-brotherly attitude, however, it sparks Ruben’s jealousy. Other predictable episodes join that one. Stevie takes to smoking and drinking, and tries to hide it from Dabney. A slightly older girl takes Stevie into the bedroom at a party, introducing him to the wonders of sex. Stevie attempts a dangerous stunt before he’s ready and suffers the consequences. Dabney becomes aware of the time her kid is spending with the guys, and, believing them a bad influence, confronts them, embarrassing her son to no end. Ian encounters his brother with the crew and gets into a face-off with Fuckshit. And when Ray links up with some pro scouts, it irritates Fuckshit so badly that the group has an accident on the way home, leading to a hospital sequence that brings everybody together and allows for a montage to close things out.

That’s not the only montage in “Mid90s,” of course—there are others earlier, showing the crew and other skateboarders messing around in public places (sometimes attracting the attention of cops and security guards in the process: one especially amusing scene has a “rent-a-cop” trying to force the gang to leave a fenced-in schoolyard, leading to a mutual stream of insults but no resolution).

In these surface matters Hill’s film is actually pretty conventional, and in other hands it might have become little more than an earnest tale about not judging books—or skateboarders—by their covers. What sets it apart is its semi-documentary look; Hill and cinematographer Christopher Blauvelt shot it in 16mm in the old square-box ratio, with lots of hand-held sequences, and Nick Houy’s editing gives it a skittish quality, while Jahmin Assa’s production design and Heidi Bivens’ costumes ooze authenticity.

All that would mean little, however, if Hill hadn’t drawn wonderfully naturalistic performances from his cast. Suljic combines angelic looks with a mischievous spirit, but also a hint of the neediness resulting from his home life. Smith, Prenatt, McLaughlin and Galicia together sound nearly no false notes—even Ray’s brotherly talk with Stevie doesn’t come off as forced—while Hedges, reversing his usual good-guy image, simmers with inarticulate rage as Stevie’s poseur brother.

With its gritty visuals matched by a perfectly chosen soundtrack of pop songs and original music by Trent Reznor and Atticus Ross, Hill’s “Mid90s”—which presumably has an autobiographical element to it—is a winningly unpretentious slice of L.A. street life, with a nice taste of poignancy at its core.