It is rather depressing to think that when it comes to making films about teachers and their students, Britain makes something as trite and heavy-handed as The History Boys while the Americans come up with a film as subtle, fresh and beautifully sad as Half Nelson. It should be the other way around.

Written by Anna Boden and Ryan Fleck — who also directs — it’s a film that doesn’t fit the usual categories of the teacher genre. It’s not one of those stirring sagas about the teacher who inspires young minds to seek truth and pursue knowledge for knowledge’s sake, à la Dead Poets Society. Nor is it one of those school films that critics call “gritty urban drama”, by which they mean black high-school kids on drugs killing each other when they should be doing their homework.

Half Nelson is really a portrait of loneliness, friendship and a child coming of age while an adult falls to pieces. It is utterly devoid of sentimentality, pop psychology or big showy dramatic scenes. It has nothing really to say, but manages to show us so much. The real drama of Half Nelson goes on outside the classroom and takes place between white schoolteacher Dan Dunne (Ryan Gosling) — who is a messed-up drug addict — and Drey (Shareeka Epps), a black 13-year-old pupil.

What kind of teacher is he? The kind who arrives at school looking weary and wearing shades. Dunne, who teaches history, enters the classroom and turns off the lights, rubs his eyes and asks: “What is history?” What follows is not a discussion of EH Carr’s famous little book of that title but a young person’s guide to Hegelian dialectics. History, says Dunne, is all about conflicting forces creating change.

I suspect we’re meant to admire Dunne as a teacher, because he’s unorthodox and teaches the kids to think for themselves. But no sane parent would want him teaching their child this rubbish. There’s no sign that these kids are inspired by what he says. “Am I boring you?” he asks them. We eventually see that all this talk of change and “turning points” is ironic, for, we discover, here is a man who can’t change and break free from his drug habit. As he later admits: “I tried rehab. It didn’t work for me.”

The friendship between Drey and Dunne begins one evening after a basketball game — he coaches the girls’ basketball team — when Dunne sneaks off into an empty bathroom to smoke crack. It’s here Drey discovers her teacher slumped on the floor, holding his pipe. He looks up at her like a small, guilty and fearful little boy. She ends up placing a wet paper towel on his feverish brow. It’s not a tender moment but one that fills us with disgust and pity.

What these two have in common is loneliness. Dunne goes home to a flat that is really just a place to crash. Drey goes home to an empty apartment and micro-wave reheats for dinner. Her mother has to work long hours, her dad never sees her and her brother is in prison for dealing drugs.

They meet at a curious time in their lives. She is being pushed into a kind of premature adulthood while he is regressing into adolescence. And it’s refreshing to find a film that doesn’t try to make everything clear. We never know why Dunne is such a screw-up; what we do know is that his ex-girlfriend is right when she says: “You’re just a big baby.” He is a man torn between the demands of decency and his self-destructiveness. He is going through a kind of drug hell, but it’s conveyed without any kind of heavy dramatics. No cocaine freak-out scenes, thank you. His pain is in his vacant stare and frazzled nerves.

His personal turning point comes while giving Drey a ride home one night after a basketball game. He discovers she is friends with his dealer, Frank (Anthony Mackie). When Drey asks Dunne if he thinks she could end up in prison like her brother, he tries to do the right thing by her and tells Frank to stay out of Drey’s life. So we have a drug-addicted teacher taking on a drug dealer in the struggle for this young girl’s future.

Ryan Gosling gives one of the outstanding performances that only turn up every 10 years or so. He has that skinny-guy coolness of an Edward Norton. And it’s rare to see an actor use his face so effectively. The same is true of his young co-star, Shareeka Epps, who moves effortlessly from the disapproving scowl of the adult to the hurt of the rejected child. This is really a special film, rich with heart and laced with a bittersweet melancholy.

Half Nelson 15, 107 mins, Four stars

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