'Dental college is part of the plan. Dead people are not part of the plan!" When a group of school kids accidentally bully their bantamweight classmate to death, they turn, in desperation, to a peripheral acquaintance, Phil. Phil (Sam Crane) has been silent hitherto. Now, with a kind of autistic genius for detail, he unblinkingly riffs a complete plan, from a fabricated "pervert in the woods" story through to a memorial service: Adrian Mole meets Pulp Fiction's Mr Wolf. But the seemingly foolproof plan soon unravels when one of the girls decides to use her "initiative". (That's modern education policy for you.) Dennis Kelly's DNA asks uncomfortable questions about society's reaction to violence, especially among or against young people. It also suggests (consider the McCann case) that we're a little too keen on the default pervert-in-the-woods narrative. As Lea (Ruby Bentall) ironically exclaims: "You look dodgy - you're a murderer!"

Crane and Bentall take the laurels here. Bentall, especially, is rarely off-stage, and her chattering Lea fires off words more quickly than the most gifted rapper (albeit often with as little coherence). DNA does rather confirm the playground stereotype of quiet kids as sociopaths (presumably not part of the New Connections' playwriting remit); but it's tense and engrossing, drawing several genuine gasps from the audience.

Ruby Bentall (pictured)steals the show again in Lin Coghlan's The Miracle, as the schoolgirl, Ron, who finds she has special powers after a flooded canal dumps a statue of St Anthony in her bedroom. In a town populated by broken dreamers leading crappy, unheroic lives, Ron's gift offers respite, and before she knows it she's conducting faith-healings outside ("of") Londis.

Inevitably, some folks feel concerned and/or threatened by Ron's powers. As her herald-hagiographer, Zelda (an irrepressible Rebecca Cooper), narrates: "The problem wiv grown-ups is that they 'aven't got time to fink fings frough properly."

Ron's headmistress (Petra Letang) rebukes her for spreading false hope. She also suggests that for a girl who was, until recently, rather isolated and troubled to suddenly be chosen' by God is all a bit . . . convenient, socially speaking. And so Ron is abandoned and persecuted. Until, of course, fresh problems arise . . .

The Miracle's strength is that it's unclear how much we should scoff at Ron's Joan-of-Arc efforts. It is obvious that she does not have healing powers; she just waves her hands and dispenses common sense. And yet, her quackery seems to work. Both plays are neatly complemented by less-is-more sound-tracking and projected scenery - though The Miracle does better from its pubs, rivers and offices than DNA, where the close-up shots of Coke tins on deserted football pitches is all a bit C4 documentary shorts'.

DNA/The Miracle Baby Girl, until April 10 (most shows only include two plays), at the National Theatre s=7(www.nationaltheatre.org.uk)o 0207 452 3000.