In the autumn of 1984, I had an excited phone call from Geoff Swallow of Eastern Arts. “I had an idea in my bath,” he said. “I’d like children in a primary school to work with an author on writing a book. A real book that’s going to be published. Would you be interested? Don’t laugh.”

Those were the days when wild ideas still had a place in education, so I didn’t laugh. I was baffled, though. How could I persuade a publisher to give me a contract for an unknown book, largely written by children, with no synopsis? I rang up Marilyn Malin, former editor of the Methuen children’s list, who was then running her own publishing house.

Wonderfully, she said yes.

Geoff sent me to three primary schools in rural Lincolnshire to pick one for the project. As in the story of the Three Bears, the first was too cold (“Right, you take over while I get some marking done”) and the second too warm, with children bouncing on the headteacher’s chest as he lay on the floor. The third was Brown’s CE school in the village of Horbling, and the minute I walked in, I knew it was right. Chris Gudgin, the headteacher, met me with a ready handshake and a small black cat on his shoulders, and the children were friendly and happy, yet serious. This little school was a place that really worked.

We started in January 1985, with Mr Gudgin’s class of 21 children aged between seven and 11. (The school had about 40 pupils, with Chris Gudgin’s wife, Denise, taking Years 1 and 2.) The project would run for two terms, with me visiting about twice a week.

It was tempting, of course, to plan the book on my own and involve the school as a secondary interest, but if the experiment was to be valid the whole thing had to come from joint thinking, the children being respected as co-professionals. I did throw in a title, though, feeling the need for a starting point. How’s Business had lurked in my head ever since my youngest son, Ben, at the age of five, was found selling offcuts of rabbit fur to his classmates at a handsome profit.

The first session was sticky. The children were full of ideas, but most of their imaginings came from disembodied fantasy and lacked substance. I decided we had to set the book in the place they knew. On the second visit we went out to look freshly at the Fen landscape. It was a January morning of thick fog, and the children’s breath steamed in the cold air. We could hear drainage water trickling through pipes below the soil, and thought about the Romans, who came from their hot country to this wild, waterlogged place. Romans were a familiar concept to the children, as local ploughmen often turned up their coins and weapons. Back at school, we brewed mugs of cocoa and the real work started.

One child said his granny had come to Lincolnshire as a wartime evacuee and had married a local boy and stayed here. Everyone liked the idea that Howard, the book’s hero, could be an evacuee. We talked a lot about the war and why it had happened. We went to the old people’s home just behind the school to interview the residents about their wartime memories. The children’s parents got interested and dug out ration books, gas masks, tin hats and a stirrup pump. I drafted a first chapter and read it aloud for comments and changes. The pace started to quicken.

Local history became more and more important. We had to retrace the defunct railway that brought in coal and took out sugar beet. We discovered what types of locomotive were used, and whether it would be possible for a runaway boy to climb into a coal truck. We did drawings of local cottages, one of which would figure in the story, and the museum in Bury St Edmunds trustingly lent us a Roman chariot figure.

Increasingly, the book began to dominate all the school’s curricular work.

The children looked at the logistics of their hero’s journey back to London, reading maps and calculating distance and time. They became expert at counting in pre-decimal money. They came to understand the underlying reasons for the war and made life-sized papier-mache figures of Howard and his friend Anna, a German-Jewish refugee girl in the story. They built a full-sized air-raid shelter and learned the songs of Vera Lynn. And they wrote and drew endlessly.

When the book was published in 1987, the school held a launch party - with a special event. The local RAF station had dug out a Spitfire with some flying hours left, and we all went out to the playground and gazed up. The little plane with the pointed wings zoomed towards us out of a bright sky, then turned and swung into the “barrel roll” reserved for triumphant occasions. Several of the watching adults cried unashamedly. Half an hour later the pilot walked into the school, still in helmet and goggles. “My hero!” a little boy gasped. It was an emotional day, and in the evening the whole village came in 1940s costume to a dance in the village hall.

The book did well. It was shortlisted for the Smarties Prize and filmed by the Children’s Film Foundation, which, in turn, gave rise to a BBC documentary and a Jackanory week on television. Hodder Children’s Books reprinted it in 2002, so it is still alive, as is my relationship with the school.

Two years ago, Mr Gudgin phoned to say he and Denise were retiring and hoped we could do one more creative task before the end of term. Strangely, I was thinking about a book called The Summerhouse, in which children help a “stuck” writer get ideas, and it seemed perfect for the purpose. I went back to Brown’s, with its new generation of children, and did three days of concentrated work.

Grappling with a problem that reaches into the unknown is very different from the formula-led approach currently imposed on schools. I have long been convinced that children respond seriously if they are treated as apprentices in the writing trade, and, over the three days, the conviction emerged intact and strengthened. The children were marvellously responsive and worked like true professionals.

Luckily, the school was having an arts week, so the normal ascribing of each minute to a pre-set subject was on hold, but Mr Gudgin remarked that it would be impossible to do a project on the scale of How’s Business now.

Horbling continues to be a fine school, doubled in size now and popular with parents, but I was saddened to see the reduction in imaginative scope that has been forced on it, as I am saddened by so many visits to other schools.

The children were instantly taken with the idea of a frustrated writer holed up in his summerhouse with the blinds drawn. They drew pictures of the place, to make it real in their minds, and invented people for the story. The lead character, Chokker, came directly from a boy who demonstrated the martial arts he was studying. We had too little time to plan the plot development in detail, but in the three days we laid down a mass of material that found its way into the finished book. Most valuable of all, the children expressed some highly personal feelings and experiences through writing as fictional characters. I respected their privacy about such revelations, but their work contributed an emotional verity that the book might otherwise have lacked.

At the end, we held an evening event in the village hall, where children read their poetry and prose, sang and played instruments and laid on a “walking exhibition” of the drawings and paintings from the past three days. The place was crammed, and some of the original How’s Business children arrived, now grown-up men and women. “When I heard about this, I couldn’t have stayed away,” one of them said.

Three of them turned up again recently, when I went back to the school two years after the work on The Summerhouse to celebrate its publication. As I read the first chapter of the finished book aloud, it was odd to think that the people involved in writing this and How’s Business were aged from under five to approaching 30, not to mention successive generations of teachers.

Talking about The Summerhouse between sessions of reading, we found ourselves remembering how the ideas had piled in from everyone. There was a lot of thrilled fascination as children identified their own input - dogs turning into dragons, the invention and naming of Luma and his martial arts fantasy world, the holed-up author with a parrot called Agatha, the debate about GM crops.

I was astonished all over again by the reliable richness of creativity that lies in every child. Long may it survive.

The Summerhouse, by Alison Prince, is published by Walker Books, pound;5.99. How’s Business is published by Hodder Children’s Books, pound;4.99