When Sorcha Groundsell stepped out onto the red carpet for the world premiere of Scott Graham's feature film, Iona, at the closing night gala for this year's Edinburgh International Film Festival, she posed for the paparazzi alongside the film's lead players Ruth Negga and Douglas Henshall like a veteran. In the film itself, Groundsell played a teenage girl who is carried around on her father's back after an accident left her paralysed below the knee. For a seventeen year old from Lewis like Groundsell, it was quite an arrival.

With another two short films already under her belt, Groundsell makes her professional stage debut during this year's Edinburgh Festival Fringe in Stain, a new play in which Groundsell is onstage throughout Mark Westbrook's intense drama about a star pupil's relationship with her teacher after she doesn't quite make the grade.

“She's a very interesting one,” Groundsell says of her character in Stain. “There's nothing about her that isn't complex. She starts off very bright, very motivated, and has an amazing future ahead of her as a surgeon. Then she's given a 'C' in one of her exam papers, and goes on a downward spiral. That one mistake knocks her off course and she can't cope with it. Over eighteen months she does everything she can to get the grade changed, and goes from being about to go to medical school to working in a biscuit factory and having a criminal conviction, but she must have justice for what she sees as her teacher's mistake.”

For someone like Groundsell who isn't that long out of school herself, the play's subject is “a hot topic. As extreme as the play is, having lived through a similar sort of thing, and whether the education system is or isn't at fault, I can understand that sort of pressure, and I think it's really important to raise something like this. When I was still at school I'd already decided to do acting, so my future wasn't dependent on getting five 'A's, but for other people who might have wanted to go to university or medical school it was quite scary.”

As it turned out, Groundsell did get five 'A's, which she agreed with her parents to aim for before leaving school early to pursue an acting career.

“It was the beginning of fifth year when I told them,” Groundsell says. “They were a little bit reticent about it at first. As soon as you say to anyone you want to be an actor, that's when the judgement starts, but once they realised I was serious about it they've been really supportive.”

Groundsell's pathway to acting began when, aged nine, she moved with her family from Lewis to Glasgow, where she enrolled in children's drama classes at the Citizens Theatre.

“I didn't respond well to them at first,” she says, “because I was very shy, but then I started watching films. It was Casablanca that started the ball rolling, that and Disney films. There was something magical about them that slowly opened up your imagination, even though they're completely opposite to what I'm doing now, but it slowly dawned on me that this thing I was interested in was something I could make a career out of.”

Aged fourteen by this time, Groundsell was too young for drama school, and not really knowing where else to start, eventually convinced Westbrook and Tom Moriarty, his partner in Acting Coach Scotland, to take her on.

“I've learnt everything from them,” says Groundsell. “I was fifteen when I started, and suddenly found myself working with grown-up actors, but to find teachers like that willing to work with a blank canvas, which is what I was, was amazing.”

Stain began as a project at ACS, and with Westbrook directing Moriarty, who acts opposite Groundsell, the play is produced by the pair's Tartan Spartan company. It was through her involvement in ACS that Groundsell was cast in Iona, and she has now been picked up by agents Conway-Van Gelder-Grant, whose stable includes Benedict Cumberbatch and Jack O'Connell.

Being cast in Iona was “very surreal,” Groundsell admits. “When I went into it I wasn't expecting anything to come out of it. I thought I'd have to wait something like ten years before getting a chance to do something like that, and I still get quite emotional about it.

“Iona is very like the Western Isles, so I felt I was in very safe hands up there. My character Sarah becomes a bit of a love interest for Iona's son, but because she's lost the use of her legs she has no real independence.”

Groundsell was singled out for a performance that one review described as 'heartbreaking.'

“Doing stuff like that is rare,” she says, “just to have something so complete as a female character. The more scripts I read now, the more I realise that things like that don't come around that often.”

As for the red carpet treatment, “it was weird, but lovely, and surprisingly easy to slip into, having to pose for photographs like that. You hear people complain about it, but it was great fun, and people telling you how good you are is always nice.”

Despite such deserved praise, Groundsell hasn't been carried away by all the attention.

“I want to be an actor, not a celebrity,” she says, “and if I it happens again that I end up on a red carpet then great, but if not then that's absolutely fine. I'm watching all of Jessica Lange's films just now, and of course there's part of me that wants to be doing big Hollywood films and win Oscars, but I just want to do interesting parts. I'm still learning, and anything that helps me with my craft is great. Of course, anytime I see anybody playing well in something even close to my age I want to do it. I wanna' play Juliet. I wanna' play St Joan. I wanna' play Medea – eventually. I wanna' do it all."

Stain is performed in The Space @ Surgeon's Hall to August 29.

www.thespaceuk.com