The best thing about Half Nelson, oddly, is what it doesn't do. It's a film about an idealistic (white) teacher, a latchkey (black) kid and the local (also black) drug dealer in Brooklyn. Given those facts, we can all construct a typical Hollywood movie in our minds.

But not once do first-time director Ryan Fleck and his co-writing partner Anna Boden fall in line with a lazy stereotype. Here it's the teacher who is the crack addict, and rather more in need of nurturing than the young pupil who befriends him, while the drug dealer is presented as a pretty decent, intelligent guy just doing a local job to get by.

"We understate and underwrite" is how film-school graduates Fleck and Boden put it on a DVD interview and the film's style, handheld, improvised and largely unstructured is a perfect fit of style and content. Fleck and Boden don't give you much backstory either. There's no explanation of how the adult characters arrived at their present predicament, just glimpses of their relationships and their regular working day.

This sketchy approach might not have been enough for the film without some outstanding acting. The Oscar nomination for Ryan Gosling, as the teacher coming apart at the seams, is both well-deserved and focused welcome attention on a tiny, low-budget movie (around $1m) and Shareeka Epps - expanding the part she played in the 19-minute short which is included in the DVD package - is empathetic in a quiet, self-contained role. The film leaves the emotions and details of the characters' lives up to you to imagine and, although Gilbey's role as a civil rights teacher enables the film's makers to sneak in a few germane historical footnotes (including Harvey Milk and Salvador Allende), there's no preaching on the way to a warmly satisfying ending.