The Critics: Theatre: Testosterone, testosterone, one, two, three

Sparkleshark RNT Lyttelton, London BoyBand Gielgud, London Ubu and the Truth Commission Tricycle, London

I can imagine a humour contest taking place in front of a school audience where Oscar Wilde, Groucho Marx and Woody Allen stand on one side and a 12-year-old stands on the other. The great wits would be allowed to deliver their very smartest remarks and the 12-year-old would respond only by saying "snot" or "snog" or "shit" or "fart". The result would be a walk-over. With that particular audience, only one person on stage could be guaranteed a laugh a word.

This must be a worry for anyone in the business of writing for school parties. It's an audience that arrives with its own agenda. I remember a boy at a matinee in the Olivier waiting for the auditorium to go dark and then thinking no one would notice him lighting up a cigarette. Until then, he'd never met so many ushers.

The question for the dramatist is this: how many snot-and-snog jokes is he or she prepared to make? In Sparkleshark, one of a series of plays written for young people in the BT National Connections series, Philip Ridley goes a fair distance towards meeting the audience on its own terms. Ten minutes in, the rows of green and blue uniforms in the Lyttelton were giggling as characters on-stage talk about guys and girls and snogging and playing "tonsil hockey".

Sparkleshark unfolds around the fire-escape exit on the roof of a school building. Up here, we meet Jake (Nitzan Sharron), a nerdy, sensitive type with spectacles, who is hoping to spend some time alone with his ring-binder file. He's out of luck. Half the school is heading for the roof too. The early worry in Sparkleshark is that the adults who are putting on this show are sucking up to the children who are watching it. This worry disappears when the story hits its Scheherazade moment.

The bullies are about to hang Jake and his spectacles out over the parapet when he is saved by Jody Watson's quick-thinking Polly. Borrowing a device from Arabian Nights, Polly hits on the idea of telling a story to distract the bullies' attention. Gradually the fairy-tale implicates all the characters. They begin role-playing, sharing the narrative and learning a bit more about each other.

Ridley writes this part deftly, and the director, Terry Johnson, stages it with flair. A lot of the energy comes from the rapid shifts between the fairy-tale world and the school one. The middle section is really an extended commercial for that much-cherished South Bank product, the magic of theatre.

It's round about this time that the author of the piece undergoes a strange metamorphosis. Up until now, Ridley has been larking around the playground in his baseball cap and shorts. Then suddenly he reveals himself to be a teacher in long trousers after all. As the fairy-tale winds up, we are forcibly shown the healing power of storytelling. Plop, plop, fizz, fizz! The soothing medicinal effects of narrative include creating a new ease between characters; developing a sense of community; setting in motion plans for a young-writers' group. I wish it success. One of them might write a story about bullies who listen to a fairy-tale, join in the impro, have a jolly good time, and after it is over, get bored again and return to hanging the nerd with spectacles out over the parapet.

A new musical, BoyBand - inspired by the back-stage dramas of groups such as Take That and Boyzone - opened at the Derby Playhouse in April and made its treacherous move last week to the West End. BoyBand opens with the group playing at Wembley. This prestigious venue is convincingly established in the audience's mind by one member of the band shouting out "Hello, Wembley!".

After this climactic opening, BoyBand follows the traditional showbiz storyline, going back to the very beginning as the manager recruits the lads and sets out the tough terms and conditions. That's pounds 100 a week until they cut their third album. The manager (Bryan Murray) quickly emerges as the baddie of the piece.

Essentially, BoyBand is a cross between a compilation show and a panto. The band sing and dance perfectly well, and grab whatever moments they can get to impress us with their chests and stomach muscles. There are some quick scenes between numbers. The audience boos the manager when he won't let the boys do anything. The audience cheers the band when they stand up to him.

The main irony in Peter Quilter's serviceable script is that having a number one song doesn't give you any time for sex or drugs or rock'n' roll. Out-and-out hedonists would do better to work in the box office. The manager is determined to present the boys as squeaky clean. But each of the guys gets to have his own very personal problem: I'm an addict; I'm gay; I've got a massive ego; I'm an artist and no one appreciates me; I've got a kid of my own.

We aren't encouraged to take these any more seriously - if indeed as seriously - as the costume- changes. Peter Rowe's brisk production allows nothing to interfere with the succession of songs. Each of these sound as if they've been through the same blender.

BoyBand is thankfully free of self-importance. It's a teen show that happily succeeds on its own terms. Only as the encores went on, and on again, did I respond with extra feeling to the lyrics "set me free".

As part of the London International Festival of Theatre, the South African artist William Kentridge and the Handspring Puppet Company have brought together a bizarre number of elements in Ubu and the Truth Commission. This is a strenuously anti-naturalistic production that refuses to settle into a single style. We watch actors, puppets, cartoons and film reportage. Jane Taylor's script fuses the heinous confessions of a police agent with the central character of Alfred Jarry's surrealist play Ubu Roi. She interweaves this with testimonies from the South African Truth and Reconciliation Commission, spoken by puppets. The footage of Kentridge's inky cartoons may be black and white in two senses. But the humour is black, black, black.

'Sparkleshark': RNT Lyttelton, SEI (0171 452 3000); 'BoyBand': Gielgud, W1(0171 494 5965 ); 'Ubu and the Truth Commission': Tricycle, NW6 (0171 328 1000) to 20 June