Torey Hayden has a busy morning: one of her 34 sheep has been bitten by an adder in the middle of lambing, and she is trying to coax her out of a field. The author has often described the work with children with special needs that inspired her bestselling book as “more process-oriented than goal-oriented”, and you don’t get much more process-oriented than a flock of sheep.

Her first ambition, having grown up near Yellowstone National Park, Wyoming, America, was to work with bears. To fund her degree in biology, she found a part-time job as a teacher’s aide (teaching assistant) for children with special needs and “fell in love with it immediately”. The first decade of her career in the US Midwest was split between teaching (in special education classes and supporting children with special needs in mainstream classes) and consultancy as a specialist in selective mutism. She videotaped her pupils “because I missed so much when I was working closely with them”, and watched the tapes every afternoon as she wrote up notes. “It gave me an objectivity I didn’t have in class.”

Her first and most famous book, One Child, was published in 1979. It was set in a small class of children with special needs, including Sheila, a deeply disturbed six-year-old who had abducted and brutally attacked a three-year-old boy; she poked out the eyes of the class goldfish during her first lunchbreak. It took Torey just eight days to write the story of her year with Sheila, with its frequent crises and horrific revelations about the early abuse the girl had suffered, and another six weeks to find a publisher.

At first she had no thought of publication: “I had to write it for myself because I can’t think without writing and I wanted to capture my thoughts while they were still fresh, to help me order it all in my head. When I had finished, I thought the public needed to know about this child, about the wonderful person inside and what she could achieve.”

Torey went on to write another seven non-fiction books, including The Tiger’s Child, in which she encounters Sheila, aged 13. Most were published in the UK in the early 1980s and some have been selling for more than 25 years. More than half are rooted in the highs and lows of classroom life (One Child, The Tiger’s Child, Beautiful Child, Somebody Else’s Kids, Just Another Kid, Ghost Girl) and are used in an American university’s teacher training programme.

Other books have been generated by her one-to-one clinical work. She encountered Kevin, the teenager at the centre of Silent Boy (just republished in paperback by HarperElement), in a child psychiatric unit where his mother had left him. He had not spoken for some years. Hospital staff called him “Zoo Boy” because he spent most of his days in a cage-like structure he had built under a table.

Torey worked with Kevin for more than two years, with some long breaks - such as when he tried to sexually assault her in a store cupboard. Despite this and other crises, including making a dagger to kill his abusive stepfather, she rehabilitated him to the point where he could live in sheltered housing and attend high school. Kevin now has a happy family and a job as a hospital orderly. “Of everyone I have worked with,” she says, “he is the closest to being an unqualified success.”

One Child, now available in 28 languages, was an immediate bestseller and meant that in 1980 she could fulfil a dream to move to North Wales, which she had first visited for a mutism conference.

She continued to work with mute children, and her later books include material from her experiences in Wales, although her American publisher insisted that the details were transposed to a US setting. This, and the need to protect identities by changing names, re-ordering events or creating composite characters, make the relationship between her career and a particular book hard to pin down.

“One of the biggest challenges is keeping privacy and honesty in mind,” she says. She has been meticulous about getting permission from pupils’ families and showing them manuscripts where possible, but admits that it would be hard to write a book like One Child today. Even if she could get permission to film pupils, there would be a string of other professionals to consult.

“When I started teaching there was a lot less supervision: you had more freedom and potential for finding your own way, so you could have great successes; but you could also have serious failures, and I did.” She thinks her process-driven philosophy would sit uneasily in today’s schools. “Life’s a balance between process and outcome. Education is now more inclined towards outcome - the UK is not as bad as the USA yet on this, but it’s working hard to get there.”

Inclusion

Some things do not change: the school-based books reveal long days of firefighting in class, breaks and lunchtimes spent with distressed children, and nights making resources. “It was a workaholic period of the kind that you can probably only sustain in your twenties.” In an uncanny prediction of today’s inclusion debate, she was first led out of the classroom by a shift towards placing children with special needs in mainstream classes. “Inclusion is a wonderful idealistic concept, but it was being implemented as a money-saving device. Working closely with very few children, as I had been able to do, is expensive.”

While her earlier books were “my attempt to showcase fantastic kids”, others attempted to explain wider issues. Beautiful Child, published in 2002 with a UK edition last year, explores the difficulties in identifying and acting on evidence that a child is being sexually abused. She had first visited this territory in the early 1980s with Ghost Girl, and since then has been both a counsellor and president for North Wales Childline.

“I wanted to show how difficult it is to pick up on signs even when you are seeing a child daily. When Ghost Girl was published in the UK in the early 1980s, a journalist came to interview me and said: ‘Well, it’s a terrible story, but that wouldn’t happen here’. Beautiful Child was written after the Childline and NSPCC campaigns plus all the public concern about sexual abuse. All the knowledge was there but it was still hard to identify and prove it.”

Now 56, Torey does not plan to write any more books about education. “I’ve come to the end of what I had to say about my teaching days. I haven’t taught for 20 years and it would be dishonest to set myself up as an expert.” She passes on her expertise through the Citizens Advice charity and has a fourth novel, Overheard in a Dream, coming out in June. “It’s about a nine-year-old boy who has been diagnosed as autistic, but he isn’t. So not a complete departure.”

Silent Boy is published by HarperElement, pound;6.99

Children and young people’s names have been changed.