It may not have the standing of the UK's established art schools or, like Glasgow School of Art, have produced a conveyor belt of Turner Prize nominees, but Leith School of Art is remarkable in its own way, not least for the personal histories of its founders and for the educational ethos that drove them to set up the establishment in the first place.

Nor has its position outside the mainstream lessened its contribution to Scotland's deep pool of artistic talent, as an exhibition opening this week to mark the school's first quarter-century ably demonstrates.

Run as an independent charity with no state funding and based in a 150-year-old Lutheran church that once housed the Norwegian Seamen's Mission, Leith School of Art was founded in 1988 by husband-and-wife team Mark and Lottie Cheverton, both former art teachers at two of the capital's most prestigious private schools.

The ethos underpinning the school came in part from Mark Cheverton's Christian faith but also from his belief that mainstream art colleges didn't provide a nurturing or supportive enough environment for aspiring artists. It was a belief he had developed in London a decade earlier when he and a group of fellow Christian art students would meet to discuss ways of linking their practice with their faith. Among the group was Nick Park, who would later found Aardman Animations, and Philip Archer, now the long-serving principal of Leith School of Art.

"It was the late 1970s, the time of punk and a very aggressive time," Archer explains. "We saw people being damaged in colleges because of the aggressiveness of the teaching and we reacted against that. We said 'Wouldn't it be wonderful to see a small, community-like art school that passionately believed in teaching art and also cared for each individual student?' So that became the underpinning mission statement."

Cheverton later taught art at Marlborough College in Wiltshire, where he was mentored by head of art Robin Child, father of Charlie And Lola creator Lauren. It was Child who encouraged Cheverton when, after five years teaching art at the Edinburgh Academy, he put that mission statement into action and set up Leith School of Art with his wife. The pair had met when she was an A-level pupil at Marlborough and married after she graduated from London's Slade School of Fine Art.

Archer was there the day they received the keys for what was then a disused church near the docks, bought with their own savings. "They were a remarkable and charismatic couple," he says. The school opened with 18 students, running evening classes and a Thursday session.

But three years into the project, tragedy struck. In 1991, returning from Newcastle airport and a summer holiday abroad, Mark and Lottie Cheverton were involved in a head-on collision with a truck in Northumberland and killed outright. It looked as if the school would close but, at a memorial service for the couple, Archer sounded out Robin Child and others about the project and all agreed something should be done to try to help it continue. That something turned out to be Philip Archer.

"It was a hard, hard year taking over from them," he says. "It wasn't easy but we got through that and the school gradually built up from there." Today the school has over 300 students and employs 30 people, and will soon take on additional premises on Leith Links to provide some space for expansion.

The Leith School Of Art Alumni Exhibition, meanwhile, opens on Friday at Dovecot Studios in Edinburgh. It features a selection of work from 17 former students, among them portraitist Owen Normend, filmmaker Jamie Stone, fashion designer Morwenna Darwell, graphic artist Tim Moore and textile designer Jane Keith. Each will show five or six pieces of work and the retrospective will occupy both downstairs galleries.

One of the school's most successful alumni, also represented in the anniversary show, is Glasgow-born Toby Paterson, winner of the 2002 Beck's Futures award and now an in-demand creator of public art pieces. His colourful sculptural piece Poised Array adorns the front of BBC Scotland's Pacific Quay headquarters in Glasgow and he's currently installing a work in Kirkcaldy as part of the Generation 2014 show.

Paterson was just 16 in 1990 when he caught the train for the first day of what would prove to be an eventful foundation year at the school.

"At that time I wasn't being stretched at all at school and any of the more conventional routes open in Glasgow would have been more of the same.,'' he says. ''So the decision was made to jump in at the deep end, and that worked out really well. It was an amazing year. It was a long time before I worked that hard again in a single year in terms of producing a body of work."

With the Chevertons as his sole teachers, Paterson knew the couple well by the time he left Leith School of Art and headed home to Glasgow to continue his studies at the city's celebrated art school. His inclusion in the alumni show of a selection of screenprints is in part a tribute to Mark Cheverton, at whose elbow he first learned the techniques of printmaking.

It's testament to the esteem in which he still holds Leith School of Art and the Chevertons that Paterson is willing to contribute work, though he admits it's a process which has raised bad memories as well as good ones.

"When they died there were a lot of loose ends," he says, "because you leave a situation like that thinking: 'I've just spent an intense year with these amazing people and I'm on to the next thing, but I'll keep in touch with them and our paths will cross'. That of course was tragically brought to an end. So there's definitely still a melancholy aspect to it for me."

Leith School Of Art Alumni Exhibition is at Dovecot Studios, Edinburgh, May 2-31, dovecotstudios.com, www.leithschoolofart.co.uk