Richard Frostick stands in front of a choir of small children, guiding their wavering voices through a song. Next he is at the piano accompanying a group of girls whose gospel songs are a tradition in their church. Then it's over to the jazz orchestra with drums, keyboard and saxophone, playing fast-paced beat music. In a pause, the renaissance band can be heard, melodic and vivacious.
These are children from the north London borough of Islington, accompanied by their inspector for music, rehearsing for tomorrow night's public concert at Sadler's Wells Theatre, before the theatre closes for a Pounds 30 million refurbishment.
Frostick had dashed off a letter to the theatre's management when he heard it was closing for two years - its Lottery money had come through. "It's delightful that they said yes. Children opened the theatre with a concert for Queen Mary in 1931 so, appropriately, children will give the final performance before it closes for a while."
The concert is the latest in a short tradition of summer concerts begun after l992 when Frostick first established the Islington Music Centre. Every Saturday afternoon in term-time, more than 300 children arrive on the dot of three o'clock, forsaking football, shopping sprees or hanging out with mates, to spend two hours developing their skills and playing together at the centre. Some have travelled miles across north London to get here. One boy arrives in a wheelchair. Children who are school refuseniks during the week are among the most dedicated. A headteacher observed recently that some of her more "challenging" pupils behave like little angels at the centre.
The Islington Music Centre is Frostick's "baby", a project that has grown out of his conviction that the chance to make music, and achieve excellence, should be there for all children within his borough. When the Inner London Education Authority broke up, Islington was left without a music centre for children who didn't get school music or who wanted more than that. This was "nothing short of catastrophic" to the man who had started out playing the piano at the William Tyndale primary school, moved on to become head of music at Islington Green comprehensive, was made music adviser and finally music inspector for all Islington schools. Frostick decided he would create a music centre himself.
He approached the local director of education, fired with the vision of a Saturday centre offering a musical experience which was complementary to school music teaching - "definitely not instead of" - to every child who wanted it. He envisaged children of every class and race, from the most disadvantaged with no instruments through to children who have had music tuition practically from the cradle. He wanted children who do not succeed well at academic subjects, refugee children and others, to develop their self-worth through music. But the director shook his head and regretful speeches were made about there being no budget.
"I went away very disappointed and then I thought, 'to hell with this job as inspector. I know what musical potential there is in Islington, and I'm not going to accept that things must be negative, a story of failure.' I decided I would start out by doing it voluntarily so it wouldn't cost the education department."
He wrote to the parents of the 15,000 children in the borough, inviting them to apply for the project, and he sent letters to all the primary schools. He received 1,000 replies from a total cross-section of the Islington community which convinced him that there was, potentially, a huge demand. Frostick returned to the director, said he had had 1,000 applications and was given start-up money for basic tutoring.The first 120 children were chosen on audition which Frostick says emphatically was not selection on ability - because that would have immediately prioritised privileged children who had had the chance to learn well and develop. "I wanted children with potential and real enthusiasm, but who might not have been picked up as achievers in school, and I wanted them as young as five."
The first thing he did was to form a choir "because you can teach, say, 100 children at once and it fits in with the national curriculum which has strong choral emphasis. Other than that, it was me on the piano and the recorder teacher, initially."
Since then, they have received funding to expand. They have more than 300 children forming three choirs, a jazz orchestra, a renaissance band, a drumming workshop, composing and general musicianship workshops and a series of recorder groups.
Frostick's pride is understandable as he talks of what he sees the centre achieving: "For some kids it is simply fun, an opportunity to make music with friends, but it is more than that for others. There are children for whom school isn't working and who feel very inadequate or who are close to being expelled. They come here with no baggage and they can be stars, which is very good for their self-esteem.
"I've had parents telling me how much their children have calmed down and gained in confidence. There are children who have never dared play in front of anyone and they overcome that. There are children who feel their cultural identity is a negative thing and when they come here their culture may become a wonderful part of the music we make."
And now Frostick, who is also an Ofsted inspector, is busy making further plans: "I want to establish excellent Islington orchestras; I want more centres so that we can take more children and I am determined it must be free. We've already played to raise money: we've begun to get supporters like the Arsenal Football Club, who gave a big donation, and the Sadler's Wells concert will help."
Then he stops and considers: "What's been achieved? I'd say the music has brought a whole area of meaning into the children's lives - but I'd have to say that in a non-sentimental way or I'll lose my street cred altogether."
Islington Saturday Music Centre summer concert is on Saturday June 29 at Sadler's Wells Theatre, Rosebery Avenue, London EC1R 4TN. Box office: 0171 713 6000 Dayna Byfield-Elizabeth (13) travels an hour and a half from Edmonton to attend the centre:
There's nothing like this where I live and at school the music is very limited and dull. Here you have the opportunity to do what you like and they help you achieve it. I've definitely gained confidence singing in front of other people - I never wanted to do that before. Now I'm preparing to do solo singing in a music festival.
Tom Newnham, 12, has cerebal palsy and is in a wheelchair. He started coming to the Centre two years ago: I have to put up with a lot of teasing and being patronised at school and although I give a bit of lip and it shuts people up, it makes me unhappy. I came here because I like drumming - I've been doing it since I was a toddler, banging about with saucepans. I don't get patronised at all here because I can make music and that's all that matters. I can play my part, so it's a happy experience and my drumming has improved a lot. The centre is a big thing in my life.
Mary Margaret Sullivan, 16, came to the centre on the recommendation of friends at Islington Green school a year ago.
The music at school is quite good, but among my peers it wasn't the thing to join a choir, so I never did. Here I belong and it's wonderful because everyone else is very enthusiastic. Doing well here has helped my school work quite a lot - the teachers have noticed that.