Life is always a slog in a Ken Loach film. And that's just by way of saying hello: Things then generally get worse as the dashed dreams of screwed-over working-class characters inflame the pedagogic tendencies of the committed socialist filmmaker. Yet even when he indulges in a hectoring show of documentary-style outrage (as he did three years ago in ''Bread and Roses''), Loach's advocacy on behalf of those with only threadbare safety nets beneath them feels trustworthy. In the grim and empathetic lost-youth drama Sweet Sixteen, the director focuses on a few failed souls -- rather than excoriate the system that failed them -- to produce a story of particularly streamlined, eloquent despair.
A cousin in setting and community to Loach's 1998 12-step-recovery movie, ''My Name Is Joe,'' with a Cannes prize-winning script by the same screenwriter, Paul Laverty, ''Sweet Sixteen'' follows Liam (Martin Compston), a scrappy, skinny hero with fate betting against him. The teenager hails from generations of losers in Greenock, a gray Scottish town down the Clyde River from Glasgow, a former shipbuilding center now rusted by unemployment and disillusion. Liam's mother is doing jail time, her boyfriend is an abusive, drug-pushing thug, and Liam's mean granddad wants a piece of the dealing and scamming, too: He joins right in, beating his grandson when the kid won't play smuggler during a jailhouse visit. (Subtitles for the clotted Scottish-accented English dialogue aid tremendously in the streamlining. Without them, we'd understand nowt.)
Liam isn't even the age of the title yet when his story begins, and life surely isn't sweet for him and his equally underloved mates. He gets by peddling cigarettes with his best friend and fellow truant, Pinball (William Ruane), dreaming of raking in enough money to take care of his mum when she's set free in a couple of months. The ''wee man'' is resilient and resourceful. He doesn't use drugs himself, but recognizes that selling them is where the big money is now; pretty soon he's working for a silky, lethal local don, with his hopes desperately pinned on a fantasy future of making a home with a clean, caring mother in a snug little caravan overlooking the Clyde.
It's all hopeless, of course; Loach makes that clear with every kick and punch Liam endures while still managing to believe in a better tomorrow. And a few too many miseries pile up in a plot that turns melodramatic in the last reel. Still, there's a kind of purity to Liam's self-imprisonment, as well as an unpolished power to the performances the director gets from his cast, most of them first-time actors. It's no fluke that Compston, a compelling, intense presence with a smudged resemblance to Josh Hartnett, was voted Most Promising Newcomer in Britain's Independent Film Awards. Loach may fault a heartless economic system, but Compston's Liam doesn't. Each time he hits a dead end, he makes the awfulness feel newly terrible.