The festival, still sponsored by The Sunday Times, fulfils many functions. It provides a showcase for a range of student productions; an opportunity to take part in workshops and masterclasses run by professionals; a springboard for budding professionals; and, uniquely, a chance to let loose your opinions on the actors, directors and writers in the intense daily discussions that follow the productions.
Over the years the festival's educational importance has grown, and school and youth theatre productions have been part of its landscape for many years. But a visit to the first half of this year's week-long event at Scarborough, which ended on Wednesday, prompted some critical questions.
First, why isn't the festival reflecting the high quality and range of theatre and drama work going on in many schools and among youth theatre groups, much of which is innovative, original and exciting?
The answer can to some extent be found in the statistics. This year, in an adjudicated entry of 97, only 11 were from schools, and as few as three from youth theatres; and only two in each category made it to the final programme in Scarborough.
This may of course be a reflection of the marginalisation of drama in many schools, as well as of the parlous financial climate in education and youth theatre, which makes transferring a show to the festival - a tricky enough task at the best of times - a non-starter for many groups.
Second, what exactly are the programme selectors looking for in productions involving school-age students? Shows by Burnley Youth Theatre (State of Decay) and Yarm School in Cleveland (Kiss, Cuddle and Torture) came too late in the festival to be included in this review. But the standard of the other two productions selected was disappointingly low.
The better of the two was a new play Right to Silence, presented by students of Headlands School in Bridlington, and written by their drama teacher Greg Jemison. It focused on the plight of 16-year-old Eddie, who has not spoken since the age of two after witnessing a traumatic family event, and who finds solace in basketball and soul music.
The piece - based in part on the writer's own experience of the stresses of parenthood - avoided the obvious sentimental pitfalls, and sporadically achieved a certain life and momentum in some of the devised scenes featuring Eddie and his peers.
But the enthusiastic and hard-working young cast struggled to give spark to the adult roles - Eddie's parents, the family psychiatrist, his teacher - and were not helped by a script that rarely rose above the pedestrian. The result was a worthy, unpretentious, but ultimately dull piece that never really managed to engage as theatre.
The Red Rose Chain Theatre Company, a youth group aged 8-21 from Ipswich, directed by Joanna Carrick and David Newborn, certainly deserve full marks for ambition in tackling a shortened version of Pericles, arguably Shakespeare's most difficult and erratic play.
Unfortunately the production was marred by a gratuitous and heavy-handed modernity - Pericles as James Bond, Viennese waltzes, guest appearance of Superman - that jarred with the text. While there were some good visual touches and neat ensemble work, the directors seemed more concerned to impose clever bits of business on the young actors than to help them breathe life into their characters, understand the meaning of their lines, and tell a coherent story.
The third question relates to the workshops and masterclasses. In the last five years these educational elements have become an important and popular part of the festival, especially for those teachers and students - more than 50 per cent of the participants this year - who came without being involved in a show.
From the comments of several teachers and students at Scarborough, as well as my own observations, it was clear that standards varied a great deal. Many sessions, perhaps the majority, were focused, eminently practical and stimulating. Terry Johnson's masterclass on directing, for instance, was rigorous and challenging; the BBC TV and radio workshops were widely praised; and many others were felt to be rewarding. But some workshop leaders were poorly prepared, uncertain about what they wanted to achieve, or unable to pitch their session at the right level. Students, many of whom have travelled long distances to attend, deserve better than this. One wonders whether teaching skills are being given a high enough priority when workshop leaders are being selected.
One masterclass in particular, where talk replaced action, attracted a lot of criticism. "It was self-indulgent rubbish," said one angry teacher, who attended with his school students. "It was patronising to the students, who were very critical: they soon know when someone is bull-shitting."
Happily, the main programme contained several pieces of very watchable theatre. Most absorbing was Thinking of You, a mysterious but very affecting piece from Bretton Hall College. The production of Albee's Zoo Story from the same institution deservedly scored for its excellent acting, while the taut two-hander Violent Night, from the Welsh College of Music and Drama, held its audience from first to last. These and other less successful shows were vigorously taken apart at the invaluable open discussion forums. Here, where all kinds of aspects of theatre are chewed over, the opinion of a GCSE drama student is listened to with as much respect as that of the Playwright of the Year. This is the real educational centre of the festival, where as much can be learned from discussing a bad show as a good one.
Details of next year's festival from the NSDF National Office, 20 Lansdowne Road, Muswell Hill, London N10 2AU, (0181 883 4586).