The layers at the top are still intact. The National Student Theatre Company have again succeeded in bringing the winning shows from the Scarborough Festival to Edinburgh and in doing well with them. From Hull University, Private Aye Theatre Company’s The Bald Prima Donna lives up to its glowing reviews. Director Clare Prenton’s four young actors sit around a parody of a sixties sitting room, supplementing Ionesco’s absurdist lines with absurd, but very well observed, syncopated movement. The timing is sharp, the acting, particulary from Sam Troughton, confident and accomplished.

But producing performances of this order from 21-year-olds requires a system which will give experience to 12 to 17-year-olds. Good youth theatre, though, is vanishing from the Fringe, with Nottinghamshire Education, who brought up to ten shows every year, the latest and most conspicuous casualty. Their absence leaves only Leicestershire Youth Arts presenting more than one youth show at the Fringe.

LYA manage to produce six shows a year because they have a taut house-style - ruthlessly pared hour-long versions of classics performed ensemble style. Sometimes, as in this year’s Pinnochio, the formula wears distinctly thin. Collodi’s original parable is dour, confusing and lengthy - Disney picked the best bits - and the audience were spared none of the plot twists. Once a Catholic, on the other hand, though cut to the point where some parts didn’t even make sense, demonstrated the strengths of this style - the piece was pacey and frequently hilarious. It was also extremely well acted, not just by the three girls with the plum parts of the three adolescent Marys, but by Freida Roenisch and Vivienne White, who created the Reverend Mothers, and by Mark Beavan, versatile in all the male roles.

The LYA version of Twelfth Night was a remarkable piece of summary, making sense of everything except the SebastianAguecheek sub-plot. It was also lucidly directed and beautifully played and featured a performance of intelligence and distinction from Lindsay Burns as Viola.

West Lothian Youth Theatre have the advantage of receiving the relatively generous funding still available in Scotland. They have again come up with a successful fringe piece this year - the relatively small-scale Elvis, Devil Elvis. The script - a new one by Roderick Williams - is a hoot. It is a cheerful conflation of Cinderella, Dr Faustus and Hairspray featuring teenagers’ favourite things - bad parents, black humour, stern morals and dead pop-stars.

The void left by the youth theatres at Edinburgh is being filled by an increasing number of stage schools and individual performances from private schools. They are a poor substitute. Companies such as 21st Century Fox - the Midlands’ biggest casting agency - or the Edinburgh Acting School, are dedicated to making stars, not teaching children to work together or to speak Shakepeare. The results, therefore, vary between EAS’s decent, ambitious amateur dramatics, and Fox’s toe-curlingly terible, An Alien Stole my Skateboard.

Private schools may have the money to come to Edinburgh, but they rarely have the same range of experience available to youth theatres. Gresham School’s Unman, Wittering and Zigo, for example, was an accomplished school play, but, because it had no one old enough to play the adults, could not aspire to be any more than that.

Even at the level of children’s shows, Edinburgh is suffering. Only Oxford Headlights are attempting anything ground-breaking or ambitious - a thrilling, tautly written version of The Snow Queen, which spares children nothing of the dark excitement of Andersen’s fable. But then, Oxford Headlights are a young, just-graduated company, who have benefited from a youth theatre system in full working order. It is sad that the children they are playing to will not, on the current showing, be able to bring their own shows to Edinburgh.