Ash trees rustle in the breeze while beneath them muddy children run free, collecting leaves and searching for bugs in the shadows. This must be a forest school. Or is it?

According to academics in a book, Critical Issues in Forest Schools, to be published next month, there is a high probability that it is not a forest school as, it says, large numbers of nurseries, primaries and secondaries are falsely claiming claim to be one.

The forest school movement, introduced to the UK about 25 years ago, has taken off in the last decade, partly as an alternative to the formal, test-driven infant and primary curriculum. It is seen as a way of getting children outdoors, in touch with nature and away from their phones and computers.

The concept was inherited from Scandinavian outdoor kindergarten lessons and has grown in the UK into a distinct approach to teaching and learning. The lessons are outdoors, usually in wooded areas, and are learner-centred, and play-based.

But some schools and nurseries, in both the state and independent sectors, are using the term as a marketing tool. Parents are being misled because the term is being widely used to describe general outdoor “getting muddy” activities, or one-off environmental sessions.

The authors of the book, themselves involved in forest schools, say the idea should be about discovery learning over an extended period, with children involved in meaningful and challenging activities. These should entail some risk – lighting fires, or learning to use knives, for example.

Taking children outdoors to go pond dipping, or to learn about the Vikings, doesn’t make your school a forest school, says Mark Sackville-Ford, a lecturer in education at Manchester Metropolitan University (MMU) and co-editor of the book. “Forest school sets children free to follow their curiosity, it is slightly subversive, an antidote to the results and test-driven classroom,” he says.

At St Mary’s primary, children ‘learn through play and discovery, climbing trees and using knives’. Photograph: Christopher Thomond/The Guardian

The book, a collection of papers from academics and teachers, defines the essence of forest schools, the processes by which children learn in the sessions and the challenges for practitioners.

Elizabeth Irvin, headteacher of St Mary’s primary in Stockport, which is a forest school, and a contributor to the book, says not all schools are in it for the right reasons. “The saddest comment I heard was by a headteacher who said ‘I can’t afford not to do it because every other school around me is doing it and it looks good on your website’,” she says. At St Mary’s, the principles of forest school are embedded for each year group.

Businesses have been set up offering “forest school experiences” and training, claiming they improve pupils’ self-esteem and promote healthier lifestyles. Even companies selling products such as rubber boots and waterproofs are jumping on the bandwagon, with one telling teachers that all they need to do to become a forest school is “simply take your lesson outdoors”.

Mel McCree, a lecturer in early childhood studies at Bath Spa University, has coined the terms “FS full-fat” for forest schools that follow the principles, “FS lite” for ones that try but don’t succeed, and “FS ultra-lite” for those that are forest schools in name only.

Schools are under increased pressure to perform, and at the same time under budgetary pressures, she says. “In such a climate it is little wonder that settings may use FS lite as part of marketing to compete for new business [children] and that practice can be reduced to a tick-box exercise in this cynical but pragmatic approach.”

The Forest School Association (FSA), the professional body in the UK, promotes six principles on which sessions should be based.

Not all of its 2,000 members will be leading a full forest school, says Gareth Wyn Davies, its chief executive. There are forest school leaders who are trained and committed but cannot deliver because their schools don’t have the money, or won’t devote the time to it, he says.

The forest school ethos involves risk-taking and child-centred learning. Photograph: Christopher Thomond/The Guardian

“In addition, the term ‘forest school’ has taken on a life of its own. People are calling anything outdoorsy a forest school when it should be something held over a long period of time, be about child-centred learning and be engagement with the natural world,” he says.

“It focuses on children being guided by their own curiosity rather than completing tasks set by the teacher. They are learning through play and discovery, collaboration and risk taking, climbing trees and using knives.”

Forest schools should be offering children another way of learning, says Sackville-Ford. “In the education system at the moment when all that seems to matter is the Sats score, being a forest school gives legitimacy to other things.”

What stands out in his memory is a 10-year-old boy who had little status in the classroom with his more fortunate peers. “It was quite a prosperous area and he was less successful academically and dismissed by many of his peers. In the forest school environment, when he could shin up a tree and light a fire in seconds, his peer group suddenly changed their approach to him,” he says.

However, despite the anecdotal evidence of the benefits, there is a lack of formal research findings, says Mark Leather, a lecturer in outdoor education at the University of St Mark and St John, in Plymouth. He conducted a study of forest school research and reports in his paper – A critique of forest school: Something lost in translation – that he found no reliable evidence that it improved pupils’ confidence and self esteem.

“I’m a great fan of the forest school movement and the way it seeks to provide a badge of quality but the commodification of it has created problems, including the tendency to make claims for the benefits that overreach the available evidence,” says Leather, a founder member of the British Education Research Association’s new Nature Outdoor Learning and Play special interest group.

Done properly, the benefits are there for all to see, says Helen Davenport, a lecturer in primary education at MMU and a co-author of the book.

“Being sat around a fire, being fully immersed in whittling a spoon, erecting a shelter or seeing a pupil in a new light can all fuel romantic thinking about alternative approaches to education,” she says. “You see children building a shelter with tarpaulins, sticks and ropes or making face paint out of nettles and some making bracelets out of saplings. It’s so calm. It’s magical.”

On the other hand, she knows of sessions where what goes on inside is brought outside: “I’ve see written work from the classroom brought outside with worksheets and, on one occasion, desks as well,” she says. “That is not forest school, nor is it when the children come out to find laminated posters stuck to trees with number challenges and marker pens.”

Critical Issues in Forest Schools by Mark Sackville-Ford & Helen Davenport is published by SAGE. To order a copy go to guardianbookshop.com.