Badnuff, Soho Theatre, London

"This isn't normal behaviour," says a teacher in Richard Davidson's play. It's a rare use of understatement in this drama about an institution for teenagers expelled from normal schools. Patsy has stolen a baby. Lanny has beaten up his headmaster. Brendan talks non-stop about his sexual fantasies and, as the teacher says, "likes to give himself an airing from time to time". Jay has broken both the arms and several ribs of a teacher at her former school.

The air at St. Peter's Educational Centre is dense with resentment, threat, and obscenity, which do not stop at the classroom door. Trying to teach English to these four, the young, middle-class Maggie (Raquel Cassidy) uses the tactics we have seen many times before in real life or other dramas of the blackboard jungle: she fines the students for swearing; she asks them to call out the vilest words they know, then imposes a ban on bad language (it lasts about 30 seconds); she says she will call Tom, the headmaster, to sort them out.

None of it stops Lanny from leaping atop Brendan and pounding his face. But Maggie's sympathies are with Lanny, whom she has been trying to send back to his former school so that he can continue his education. To keep Brendan from complaining, she agrees to let him visit her at home. Not the wisest move - they are interrupted by Tom, her lover.

As far as I can tell from newspapers, the streets, and public transport, Davidson, a former teacher, has portrayed the teenagers accurately - the mixture of sullenness and hyperactivity, the occasional rough wit: "Friction is what you get when you shag Pats," Brendan says, explaining the difference between two words. "Fiction is when you say you enjoyed it."

Davidson also shows us (via that useful cliché, the students reading aloud their autobiographical compositions) the reasons behind their anger. Faithful to classroom-rage dramas, the play also includes a climactic scene with a flick-knife and a sweet closing fantasy in which the "children" engage in innocent play.

While dealing with the teenagers the play is believable, if unexceptional, but its treatment of the two adults is full of holes. Too soft to prevent serious assault in her classroom, Maggie is self-protective with her lover to the point of condescension - coolly rejecting his proposals of marriage, yet indignant, when his wife learns of their affair, that he isn't sufficiently sympathetic with someone she "knows and trusts".

But, instead of being shown up as a naive do-gooder or a cold careerist (if she isn't overwhelmed by passion, why is she sleeping with her boss?), Maggie is praised for her commitment to her students.

Jonathan Lloyd's casting of the black David Harewood as Tom causes another complication - nothing in the play refers to his race, but how could it not be a factor in the sex/power/ class nexus? Davidson may see his teenagers accurately, but he undermines his play by taking his heroine at her own valuation.

To 17 April (020-7478 0100)