Ryan Gosling has been an actor to watch ever since he played a Jewish neo-Nazi in 2001's fierce "The Believer". After floundering a bit in films like "Murder By Numbers" and "Stay" - and a rather turgid detour into "The Notebook" - the actor finally finds a worthy follow-up role as Daniel Dunne, a junior high history teacher with a vicious drug habit in the indie stunner "Half Nelson".

At the start of the film, Dan is already inches from rock bottom. As he drifts from the classroom to the basketball court (where he coaches the girl's team), it seems he can barely keep his eyes open. While he's not entirely present, he doesn't come off as an entirely bad teacher - he knows and likes his kids, and he actually has something to say about history. Change, he says, is not circular but cyclical. The irony, of course, is that he himself is caught in a debilitating cycle of drug abuse. No sooner does he dismiss the basketball team than he's crouching in the locker room with a crack pipe.

There is some light in Dan's life though in the form of 13-year-old Drey (wonderful newcomer Shareeka Epps). The child of a single mom, Drey's brother is in prison and her father is nowhere to be seen, but she does have something of a father-figure in a local dealer named Frank (a subtly effective Anthony Mackie). When Drey discovers Dan's habit, an uneasy bond forms between them which develops into something deeper than either might expect. Born out of a mutual sense of loneliness, the evolution of their relationship is at the core of this highly effective and affecting film.

The film's cast is uniformly good, but "Half Nelson" succeeds mostly on the performances of Mr. Gosling and his young co-star. Ms. Epps has a natural ease with the camera and the few times Drey has occasion to smile brighten up the screen. Mr. Gosling, meanwhile, gives a performance which is a direct descendant of the best of Edward Norton, Johnny Depp and even a young Marlon Brando. He is endlessly interesting to watch and he never hits a false note here.

"Half Nelson" isn't entirely as dire as it might sound. Like the best of films, there are moments of humor derived from the honesty of its situations. The script by director Ryan Fleck and his partner Anna Boden comes off as both improvisational and impressively tight. Only occasionally the film becomes repetitive and it ends with an odd sense of "nowhere else to go". But this might be derived from our own attachment to Dan and Drey. This too is a tribute to the film. We've gotten so close to these characters (and they to each other) that we don't want to let them go.