The show's over and the guys in sharp suits, all seven of them, are laughing and joking with one another.

Even without the applause, they know it went well. They know they did themselves, and everyone associated with the performance, more than proud.

Stewart grins and tells me the whole process has been so far out of his comfort zone that he wasn't sure if he'd actually make it into the drama workshops which resulted in tonight's show, Stand. Learning lines, performing them to an audience, was a tough call in itself. But devising a show from scratch, deciding what it should be about and then finding the words to say what was inside his own head and heart was like a personal Everest not just for him, but for all of the group.

Stewart adds that opening up, expressing ideas or innermost feelings still feels like a step outside what's comfortable – but it's a step he reckons will help him find new directions in life once he's on the outside again. He doesn't say when he's due to be released from Perth Prison. But as he stands up, keen to rejoin the visitors who came to see him in Stand, he says that the drama workshops took him to "other places in my head. As if I could have been anywhere, not here. A whole different place for me." There's a pause. "I've started writing more songs -"

Behind these scenes lies a wonderfully proactive collaboration between the Royal Conservatoire of Scotland (RCS), Carnegie College – its assistant principal Janet McCauslin has come along to watch the show – and Perth Prison itself. Quietly, and behind closed doors, this partnership has been structuring drama workshops for a considerable number of years, under the auspices of the prison's education and learning department.

Usually the performances are in-house events, but Stand (presented on Wednesday of this week) was a first. The cast, as it were, went "public" with an invited audience that included their own family and friends.

Jess Thorpe, who directed Stand, knows how much that meant to her cast, but also the pressures it brought into play. "Having that audience really adds another dimension to what's already a challenge for these guys. They're not used to standing up and addressing any kind of gathering. But they wanted to do a piece about freedom of speech. And that meant being heard. Learning how to communicate, really. And that's a skill that's going to help them when they leave here.

"I know people can be very scathing or dismissive – even resentful – of arts practice being offered in prisons. But you then have to remind them that these men will, at some point, leave here. What kind of person do you want to have returning to the community? I think you have to recognise that these workshops aren't an easy option for offenders, they're not an indulgence: they're an investment."

Thorpe – co-founder, with Tashi Gore of Glas(s) Performance and Tramway-based youth collective, Junction 25 – has been the RCS presence in this, and other prisons, for five or six years now. Indeed she's now a lecturer in arts and justice at RCS where her practical experience feeds into students' course work.

Stand, meanwhile, is the culmination of 20 weeks of workshops that Thorpe has been leading, using the same task-setting and devising strategies that she uses with the teenagers in Junction 25, or – as is currently in process – the residents of Albert Drive as they prepare for a Tramway performance in July. Know what? Her cast of seven spoke as directly from the heart – and delivered the expressive movement sequences – with the same unaffected polish and humanity that makes Thorpe's other endeavours such class acts.

Last word goes to Mike Inglis, governor at Perth Prison. Watching as cast, audience and support team mingled over scones and juice, Inglis spoke of the difference the drama workshops made, not just to individuals but to group dynamics within the prison. "We see these men on a day-by-day basis, so we see first-hand how learning to communicate, learning how to express themselves, brings about the kind of changes – life skills – that they'll need on the outside.

"A show like Stand touches on issues – being ignored in a classroom, not being able to use words or say what you mean – that didn't cause any far-reaching problems for many of us. But this is new ground for these offenders. And to see them standing up, speaking movingly or humorously – just confidently – is why we appreciate what Jess, RCS and Carnegie College are achieving here."

Theatre