Summer blockbuster season is upon us, and, while Harry Potter rises like a phoenix for his latest term at Hogwart's, other magic is afoot. Because Scottish Youth Theatre's summer residency has this year conjured up the premiere this side of the border of Philip Pullman's His Dark Materials trilogy. First presented on stage in 2003 by London's National Theatre, this epic two-part quest clocks in at a mammoth six hours. Such a marathon would be hard work for seasoned professionals to sustain. For a group of young people with only limited stage experience, it's an even greater challenge.

Yet, according to Scottish Youth Theatre artistic director Mary McCluskey, who directs the first part of Pullman's epic, despite rehearsing 12-hour days, the huge cast have risen to the occasion.

"It's such a big story," McCluskey says during a tea-time rehearsal break, "and such a big journey that the two young people who are the central characters take. We always try and choose plays for the summer festival that the participants might not do in their own youth theatres at home, and try to do something a bit more challenging. I think the company from day one thought, my goodness, how are we going to be able to achieve that?' There's so much in just the first part, never mind the second, and it's been great seeing everybody just go for it, and to watch the confidence of the actors grow. Physically it's a huge undertaking, but emotionally, too, to ask people that age to stretch themselves in that way."

The appeal of His Dark Materials isn't difficult to fathom. A classic fantasy quest saga involving demons, witches and multiverses with an anti-establishment, anti-authoritarian and some might say anti-Christian bent, if one wanted to be cynical, one could argue that any stage adaptation of such a work is going to grab audiences already knee-deep in its labyrinthine plot. One could argue too that, despite this, the cinema screen, with every larger than life hi-tech special effect at its disposal, could do such an awfully big adventure justice in a manner that simply can't be replicated onstage. McCluskey, however, will have none of this.

"Absolutely not," she pooh-poohs. "There's nothing better than seeing that live connection with what's going on onstage and the audience. Anything's possible up there. Yes, people can play computer games on their mobile phones or whatever, but the live thing is what counts. Also, there's absolutely no reason why you shouldn't do something like Harry Potter on stage, and here some of the things that are raised are really relevant.

"Many of the concepts and issues in the play are at the fore of teenagers' minds. There's a sense there of young people being at odds with the world. There's the dawning of first love, the loss of innocence and the gaining of knowledge and intelligence, and what comes from that. Other interesting issues are ones about seeking to please your parents and standing up to them.

"All this is going on, and these books have been damned by the right wing in America, which is very telling, because the authority in the books is eventually killed. It's interesting here, because, for the first few days, as some of the young people are so used to working in a school set up, where there's a right and wrong answer, they're inhibited by that. After a few days here, once they realise they can say what they want, that goes away."

Youth theatre is undoubtedly thriving in this country today. When McCluskey arrived at SYT, however, it was a very different story. Youth theatre was something throwaway, considered a second-class citizen to the professional theatre world, under-resourced and under-exposed. Today sees a very different story. Yet, while most theatre buildings have invested in a thriving network of youth theatre groups, more significant is a welter of activity at a grassroots community-based level that exists largely beyond the radar of SYT and other theatrical institutions.

Perhaps in response to that, the last few years has seen SYT move away from the junior showtime approach to their summer productions, with meatier fare being gradually introduced to its programme. While conscious of not wishing to come over as desperate to appear streetwise, this is nevertheless a deliberate strategy by McClusky, and, by changing the age ranges of those involved, it is recognition that 12-year-olds and 21-year-olds have completely different social and cultural agendas.

"We have a line of progression," says McCluskey, "which I suppose is like a pyramid. At the bottom of that there's the social development thing, then at the next level there's people who might want to take drama a bit more seriously. At this stage, with His Dark Materials, it's young people who have come through all these different levels and are really serious about doing it. I'd like to think that young people are allowed to grow naturally in structures like that."

Despite such high-profile main stage shows as His Dark Materials, McCluskey acknowledges that, while putting a full stop on the summer camp feel of SYT's annual residencies, for the participants it's the experience of the previous five weeks that's the most important thing. "We've also got an ensemble coming in next week, who've done a foundation course, but aren't quite ready yet for the summer school. They'll have a week's rehearsal, and while they won't have the main parts, it will give them the chance to look at what's going on so they can see what they might want to aspire to."

During her 15-year tenure, McCluskey has made efforts to siphon out those who use working in youth theatre as a showcase for themselves and a stepping stone to "real" theatre.

"We've been chipping away for years to get youth theatre recognised as a legitimate place to work, McCluskey points out, "and there are some people who still ask me why I don't want to go into real theatre. Well, actually, I am working in real theatre, and I get to do things in youth theatre that I wouldn't be able to do. I've got a cast of 24, with another 19 joining next week.

How many theatre companies get that sort of luxury? I have a great passion for watching young people develop. There's no greater feeling than seeing someone on day one with no confidence becoming far more confident by the end of it. Not as an actor. That's not what's important. But as a person."

His Dark Materials, Parts 1 and 2, is at the Citizens' Theatre, Glasgow, July 25 to August 4. For dates and times, visit www.citz.co.uk