Are you experienced?

Plenty of performers enjoy long, rewarding stage careers without ever appearing at the National Theatre, let alone in new work by Britain's leading playwrights.

So certain Equity members will be casting green-eyed glances at youngsters from Hull, West Lothian and Surrey who next week will follow up the stresses of GCSEs with Olivier and Cottesloe debuts in plays by Peter Gill, Sharman MacDonald and Alan Ayckbourn.

Their opportunity comes through BT National Connections, the largest youth theatre project in the world. Since 1994, more than 30 dramatists have been commissioned to write plays for actors aged 11 to 19, with casts of between five and 50. The scheme was devised by Suzy Graham-Adriani, the National's Producer (Youth Theatre Projects), to tackle "the dearth of strong scripts" for this age group. "Most youth groups rely on devised pieces," she says. "I wanted to create something that would get young performers and audiences across the country involved in new writing."

In a rare misjudgement, even Richard Eyre, then director of the National, misread the signals. "You're going to fall flat on your face," he told her. "The writers won't do it." Wrong. The two previous National Connections line-ups included Wole Soyinka, Bryony Lavery and Liz Lochhead, and this year's list includes Dario Fo and Germany's Tankred Dorst in addition to Ayckbourn, Gill and MacDonald.

More than 1,000 school and youth groups applied this year, an array whittled down to 150 productions in 10 regional showcases, held during the spring at venues such as Theatr Clywd, Nottingham Playhouse and the Lyric, Belfast. Twelve were chosen for presentation at the National, balancing quality alongside the need to represent all 10 plays and regions.

Ayckbourn has been writing for young audiences for decades, but what tempts other writers to work at this notoriously low-budget and kudos- free end of the theatrical spectrum? Graham-Adriani points to their being paid "the going rate" for a one-hour play: "Plus, it's guaranteed to be produced at the National and published by Faber and Faber." Even more to the point, when most theatre commissions demand a budgetary ceiling of around six actors, the opportunity to write for vast casts represents unimaginable freedom.

Nevertheless, Gill, author of distinctly adult dramas like Certain Young Men, seen at the Almeida earlier this year, took a lot of persuading. "In a long career I had never even considered writing to commission," he says. "But I admired the scheme and thought this would be a good exercise. I wanted to write about 16-year-olds, but I'm in my fifties and felt I didn't really know how they speak and behave. I worked for a week with members of the National's youth scheme, talking and doing bits of Shakespeare. I found that, compared to when I was 16, certain taboos are no longer taboo, but teenagers are just as fragile emotionally. After that, I knew I could write the play.

"I was determined not to write a teenage allegory - something for parents and teachers to feel pleased with. The actor in me wanted to write something for young performers to get their teeth into, but at first I worked too schematically - making sure there would be enough decent parts to go round, with even numbers of boys and girls. It would have ended up as a theoretical exercise, not a play," he says.

What emerged was Friendly Fire, a moving and sometimes magical snapshot of sensitive, painfully inarticulate working-class youths in an unidentified city. Says Gill: "Crudely speaking, these boys see the colour red in the same way as the Prince of Wales's children, but they do not have the sensibility to express themselves as fully."

The main focus is on Adie, gay and hopelessly in love with his straight best friend, Gary, who's in love with Shelley, who loves Adie. As he hoped, these are terrific, demanding parts, and it's unmistakably a Gill play, with the leads echoing the concerns of young characters in his earlier Small Change and Cardiff East.

Watching two of the nine productions (including one by West Lothian Youth Theatre which is heading for the National) was a "lovely", oddly objective experience, he says: "I normally direct my own plays, and when I do, a bit of me thinks: `Well, I've directed this pretty well, but is it any good as a play?' With this, it was very refreshing to watch and think: `Those girls have caught it brilliantly, but the others are taking it too seriously.' It gives you a sense of your own potency as a writer and the variety of interpretations people put on your work."

Observing untrained actors has also been the most surprising aspect for Sharman MacDonald, best known for When I Was a Girl I Use to Scream and Shout and The Winter Guest. Her play, After Juliet, is written in blank verse, picking up where Shakespeare left off, with the Capulet versus Montague rivalry horribly sharpened by the spirit of vendetta, and Rosaline, now forlornly pursued by Benvolio, refusing to accept that the star-cross'd lovers' deaths should end the feuding.

Having seen 12 of the 23 regional productions, MacDonald suggests: "When professional actors play children, they tend to add layers instead of stripping them away. But teenagers don't really play sub-text, and have an extraordinary emotional openness. "The group from Strode's College, Surrey, took things much further than I'd envisaged. They've added simulated sex, which works well, and taken an exchange about tea and made it a euphemism for heroin, which they `cook' on stage. I had thought of that possibility and was thrilled that somebody interpreted it that way."

Even with a hit like When I Was a Girl..., MacDonald would probably have to wait five or six years to see a dozen different productions of her play: with the BT project, she saw that many in weeks: "The variety of approaches - punks versus glam rockers in one production, surfers in the next - has made this an amazing experience. More importantly, it's provided such riches in the lives of the children I've talked to."

Her enthusiasm is tempered by the fact that BT has decided not to renew its pounds 600,000 sponsorship. It will be a terrible shame if a new patron cannot be found. For now, the legacy is 34 plays, published and ripe for revival. Less tangible is the benefit to those in productions which, at a conservative estimate, have involved at least 10,000 children and been seen by perhaps 15 times as many classmates, parents and relatives - many of them attending a new play for the first time. If BT's prospective successors canvass opinion in the right places, they will be greeted by an immense chorus explaining why it's good to sponsor.

7-13 July, NT (0171-452 3000). `New Connections 99', a collection of the plays, is published by Faber and Faber, pounds 12:99