In the corner of a school garage, hung with old bikes waiting to be mended, a young man is singing as he strums a guitar. Beside him a woman plays the keyboard.

This is no ordinary jamming session to while away a school lunch-hour. The music is strong and heartfelt, but as you listen, its unusual character becomes apparent.

The man is not playing chords on the guitar, simply strumming open strings; and the woman at the keyboard pauses every so often in her playing to build a musical dialogue with him. The two look at one another, they listen. The man improvises a song around things which clearly matter to him.

Dave (not his real name) is 21 and has Down syndrome. Because of his difficulties he has been allowed to stay on at Cottenham village college in Cambridgeshire. Philippa Derrington is a music therapist who has been working and playing with Dave at his mainstream school for more than a year.

Dave has a good tenor voice and much music inside him. But when he began weekly music therapy sessions, Philippa Derrington says, “He wasn’t fully aware of me playing”. Then he began to improvise with her - on drums, guitar, harmonica - and to make up his own songs.

“In the last six months the exciting thing is that the interaction has been much more tangible and a more mutual musical relationship has developed so that he understands that two of us are making music. I want him to share it, and to know that his music is heard... Often he asks if he can stay all day.”

Ms Derrington spends two days a week at the college, working one-to-one with 15 pupils from its large social inclusion centre. Some, like Dave, have special needs; others have emotional and behavioural difficulties and need support to help them reintegrate with their peers; a few are on an alternative programme because they have previously been excluded.

Music therapy gives Dave an outlet within a therapeutic framework that encourages the safe expression of conflicting, troubling or even violent feelings. Some of the teenagers often like to play guitars and drums in the sessions - sometimes writing their own songs, or playing as if in a band.

But the skill of the music therapist is to play alongside them and support them -Ms Derrington plays saxophone and clarinet as well as keyboard - in such a way that their musical utterances are heard and responded to, interwoven in shared music-making.

“The important thing is that they are listened to,” says Ms Derrington.

“It’s an experience of being heard, and then listening back.”

Music therapy is already established in many special schools, but for it to find a place in a mainstream secondary school - furthering the cause of inclusion and helping pupils with a wide range of needs - is a significant departure.

In Cambridgeshire, music therapists are employed by the county council through the Cambridgeshire Instrumental Music Agency (CIMA), and their services are then bought by individual schools (at a cost of around pound;1,000 a term, for three hours a week).

At Cottenham village college, Sue Raven, deputy head and Senco, would like to invest in more music therapy in future, “as well as offer it in a more appropriate place than a garage”.

Philippa Derrington also works for three hours a week at Cottenham primary school - making the village probably the only one in the country to have a resident music therapist in both its primary and secondary schools. At the primary, music therapy was first requested two years ago by the parent of a child with autism, and Ms Derrington’s work was funded initially by local donations and help from the music therapy charity, Jessie’s Fund.

Then the school decided to offer music therapy sessions to a group of three children, all of them finding it difficult to communicate and to concentrate. A year of lively sessions with percussion instruments helped these children to listen, to share, to focus, to take their turn.

“All of them became more confident and able to express themselves,” says headteacher, Jan Wright. “They benefited so much, I couldn’t believe it: I had been quite cynical about music therapy before.”

Ms Derrington has also worked successfully with bereaved children. “Music therapy creates a safe space where they can use the instruments in any way they want to support expression,” she says. “I think it helps that it isn’t verbal; often it’s the non-verbal aspects of these interactions that help.”

As more teachers at Cottenham see what can result from music therapy, more are asking for their pupils to be referred, says Jan Wright.

Next year, the school expects to part-fund the work out of its own budget.

“But I know my governors will be more than happy, because we have seen the benefits.”

For more information about CIMA, tel: 01480 831695; www.soundsamazing.org