Musical director Francis Cummings takes his place in front of the 40-strong orchestra and raises his arms, poised to launch into Henry Purcell’s ‘Rondeau’ from the Abdelazar Suite. ‘No counting to three, because that’s for children,’ he says. The musicians duly burst into the opening bars without missing a beat.

Nothing unexpected there, except for one thing: counting to three may be for children, but not one of Cummings’ players is older than 12.

‘They treat us like grown-ups, like mature people,’ says cello player William, on the day before his 11th birthday. The children return the compliment with their impeccable behaviour.

Even at this early rehearsal, it’s astonishing to see such young musicians perform with so much precision. It was more astonishing still when, on 21 June 2012, they took to an outdoor stage in the shadow of Stirling Castle as the opening act of the Big Concert, conducted by the exuberant Gustavo Dudamel in front of a national television audience.

Some of them even stayed on stage to join the 200-strong Simón Bolívar Symphony Orchestra for the overture from Beethoven’s Egmont. How it is even conceivable for a primary school orchestra to share a stage with such internationally celebrated company is down to the pioneering Big Noise project. Based in Raploch, a short walk from the centre of Stirling, this £3.8m scheme was launched in 2008, drawing on the inspiration of the same ‘El Sistema’ philosophy in Venezuela that produced the Simón Bolívar Youth Orchestra.

In a community of only 3000, there are 450 children under the age of 12 who have joined after-school rehearsals up to four nights a week. By working collectively and intensively, they are able to race ahead. Even some of the youngest are able to sight-read. Everyone learns together, no one is turned away and the results, both musically and socially, are breathtaking.

‘They took to it straight away,’ says local volunteer Cath, who has watched with pride as her five children have taken up flute, percussion, viola, violin and cello. ‘It’s changed them completely. It’s brought them closer. Before they used to bicker, now it’s just singing, dancing and playing their music. They’re a lot more settled, a lot more focused … it’s brought a new light everywhere.’

The Big Noise approach is to treat the orchestra, with its need for cooperation, good behaviour and sharp focus, as a learning ground for being a responsible citizen. It’s something fellow parent Charlotte has seen in practice: ‘They’re a lot more disciplined and have more respect towards people,’ she says. ‘When they’ve got a concert, they’re like adults – they’re sat there and quiet. It’s amazing.’

This afternoon, it seems every room in the Raploch Community Campus is vibrating with musical activity. In the school hall, the youngest class is sitting at primary-coloured music stands while violinist Guido de Groote introduces them to notes and rests. To answer questions, they raise their bows in the air. ‘That’s the best bow hand you’ve ever had,’ he tells one little girl.

In a nearby classroom, the next age group is working its way up the scale of G major in the hope of winning the Kit Kat taped to the whiteboard by cellist Josip Petrac. When he tells them it’s time to move on from a harmony exercise, all 30 of them groan in disappointment.

With a generation of sight-reading musicians about to hit secondary school, the possibilities for the future are mouth-watering. Bolstered by the success so far, Big Noise has ambitions to open three children’s orchestra centres in 2013. ‘Heaven knows what kind of hip hop will come out of here and genres of music we’ve not even heard of yet,’ says George Anderson, one of the Big Noise team. ‘What will these kids do when they know how to arrange a string quartet and put samples on it and use beat boxes?’