Insolent schoolkids and educators with the stamina and sensitivity to reach them is a sentimental formula so familiar, it could stand a pantsing in the hallway between classes.

Which makes it a good thing that “Steve,” starring Cillian Murphy as a dedicated, troubled head teacher at a struggling reform school for chaos-inclined teenage boys, brings a raucously corrective attitude to bear.

Teachers are sorely undervalued in this world, and a more thorny, realistic view of the profession’s challenges has made its way into the culture of late, between the Oscar-nominated German film “The Teachers’ Lounge,” Hirokazu Kore-ada’s “Monster” and Netflix’s Emmys-gobbling hit “Adolescence.” And while “Steve,” which takes place over a day, is ultimately too messy itself to measure up to those more tightly coiled efforts, its energy makes a statement, as if the legacy of the late, system-smashing British director Alan Clarke were close at hand.

“Steve” marks the second feature collaboration between Murphy and Belgian director Tim Mielants, following their excellent 2024 adaptation of Claire Keegan’s story “Small Things Like These.” This one, too, derives from a book — “Shy” by Max Porter. In adapting his own work, Porter shifts focus from his novella’s title adolescent, a disturbed soul in mid-tumble, who in the film is still a central figure (vividly rendered by Jay Lycurgo), to the teacher character for whom the movie is named, which the Oscar-winning Murphy turns into another immersive portrayal of dark-hued, guilt-flecked intensity.

Steve’s compassion is the beating heart of Stanton Wood, a privately bankrolled school in an old manor in the English countryside, whose core staff — including Steve’s plain-talking deputy, Amanda (Tracey Ullman), and unflappable therapist Jenny (Emily Watson) — are committed to its last-chance ethos of pulling unhappy delinquents from the brink. But this is Britain in 1996 and these hot-headed young men (played by a lively mix of first-timers and experienced actors) prefer the numbing tempo of drum and bass or a well-timed punch or thrown object.

Stopping fights is a full-time a job, and Steve’s chummy de-escalation style attests to how much he cares. But on top of the day’s regular behavior management, there’s also a prying documentary crew, a visit from a local MP (a perfectly pompous Roger Allam) that goes south and what turns out to be a bad-news report from the school’s wealthy backers. When Steve explodes on them, one senses his volatile students have been teaching him something too.

And yet “Steve,” sincere in its hardcore concern, believably acted, is too scattered and schematically plotted to fully pull us into the emotional toll and scruffy joys of this work. Its social realist roots are kept from growing the more it relies on visual/sonic turbulence (hallucinatory images, a flashy drone shot) and narrative shorthands (the overdone documentary framing).

But when “Steve” zeroes in on its characters — Shy on a disturbing call with his fed-up mum, Steve fighting his own demons or in the zone — the movie captures the electric hum of unpredictability and vulnerability. At its best, we understand why these people want to keep the lights on in a dark, unforgiving world.