Fifteen-year-old Liam (Martin Compston) turns "sweet 16" the same day his mother will be released from prison. Before that day comes, the boy is determined to raise enough money to buy her a nice little caravan (trailer) overlooking the sea. To that end, he steals heroin from his brutish drug-dealing stepfather and goes into business with his buddy, Pinball (William Ruane).

They do so well that the local drug lord co-opts them. It's a profitable but precarious situation. Just as Harvey Keitel had to deal with Robert De Niro's reckless loose cannon in "Mean Streets," Liam must keep the goofy, unrealistic Pinball away from the boss, who'd rather shoot a mouthy, irritating kid like Pinball than deal with him.

Directed by Ken Loach, "Sweet Sixteen" takes place in Greenock, a dour, used-up Scottish town near the coast. Loach likes to use non-actors -- including his young lead -- and the locals' accents can be so thick that the dialogue is often difficult to understand (hence, the subtitles).

However, the hopelessness inexorably engulfing this tough, vital kid is all too understandable. Flush with the can-do idealism of youth, Liam believes he can make everything all right for his mother, for his single-mom older sister, and for himself. Watching his innocence being trampled into the dirt is a sobering experience.

As usual, Loach tends toward didacticism, underlining points he's already made. His movies -- "My Name Is Joe," "Ladybird, Ladybird," to name some good ones -- are harsh social commentaries, done with a humanist's eye for tiny glimmers of hope and humor. His relentless quest for utter realism is admirable, but it can also be off-putting and one-note.

Still, there's a raw, uncensored power here -- in the film in general and in newcomer Compston in particular. Grim yet sympathetic, "Sweet Sixteen" is a hard-luck coming-of-age story in which every ensuing misfortune stings as much as the very first one.