How can teachers introduce forest school principles to their curriculum?

On the wooded edge of an Essex field on a bright spring morning, a group of three- and four-year-olds in wellies and waterproof suits are gathered at the foot of an elder tree. "Good morning Mummy Elder," they chorus. "May we come in?" A breeze shakes the branches, and the members of Ashdon Preschool Forest School flock into the woodland for another morning of stream-jumping, log-balancing, campfire cooking and a myriad of other playful forms of outdoor learning.

The pre-school, just celebrating its third birthday, is part of a steadily growing forest school movement developing throughout the UK. Ashdon is what some might call hardcore: it has no building or indoor area at all and, uniquely in Essex, exists entirely in the wood, where – thanks to its increasing popularity – 15 children now explore, climb, jump and learn three mornings a week, rain or shine.

More commonly, forest school is part of a bigger educational mix in which pupils enjoy time outdoors perhaps once a week, but the same principles apply: a drive to build young people's independence and self-esteem through experiencing the natural world. Lili Pluck, forest school assistant at Ashdon, says: "It's about learning to realise what is around you, appreciate nature and enjoy the freedom, space and sense of peace."

Forest school is often misunderstood: it can be misinterpreted as a brand or kitemark for a school that takes its pupils outside occasionally when in practice it has a more fundamental meaning, according to John Cree, chair of the Forest School Association. Forest school isn't a badge or indeed a place – instead the name refers to a philosophy in which students work outside regularly in an outdoor natural space over a long period of time (often a year) to build confidence and creativity.

Drawing on nineteenth century European pedagogical theories on the importance of outdoor learning, and more recently on Scandinavian principles of open-air, play-based education, the ethos has grown in popularity in the UK over the past two decades in parallel to growing concerns over "cotton wool kids" overly protected from risks and rarely exposed to nature.

For all but the most die-hard cagoule-refusers, the notion has a certain idyllic appeal, but how exactly should schools go about introducing forest school principles into their curriculum? Cree, who even points out an owl hooting as he stands outdoors during an evening phone interview with the Guardian, offers some tips:

Take things gradually. A school not currently involved in outdoor education should not try to move straight to a forest school ethos, Cree says. "Get outside a little bit more regularly, maybe just in the school grounds and still be a little bit teacher-led. Start small and just gain confidence." Many organisations can help with resources: try Learning Through Landscapes, the Council for Learning Outside the Classroom, or the Institute for Outdoor Learning.

Train in-house forest school leaders. "If you want to get out into the woods on a regular basis, delving into a lot more of the practical stuff and actually building your own classroom outdoors, then train up a forest school leader," says Cree. That way outdoor learning will integrate with what happens in the classroom, and in the long run it will be cheaper than bringing in a leader from outside the school. The total training process will take about 10 months and lead to an accredited qualification – forest school practitioner level 3 – which allows the holder to run a forest school. The Forest School Association is working on a quality assurance scheme to endorse high quality training.

Make sure senior managers are on board. The headteacher and management team must be supportive of forest school principles, which should be integrated into the school development plan. Look at how you can make the most of the ethos and facilities within the formal and informal curriculum of the school. All kinds of schools can benefit, including special schools and pupil referral units.

A corner of the school field isn't enough. You need access to green space with quite a few trees, Cree says, though it's not the case that forest schools must necessarily be in woodland. "It could be a park, but a little bit of wild space helps – it gives the chance to get hidden and lost." Even schools in the countryside often use a minibus to get pupils to a suitable area.

Don't be daunted by risk. "There's a perception that forest school is all about fires and tools, so some schools get really scared and say 'I'm not touching that with a bargepole'," says Cree. In fact, whittling and fire-lighting are not intrinsic, but are often used in forest school to help children (including pre-schoolers) develop skills and learn to take and manage risks, he adds. "We're trying to get away from the cotton wool culture and when we take risks we are learning. But the training is all about helping kids take risks that are reasonable."

You won't persuade everybody. "A lot of people aren't outdoor types and you'll find a few in every school," Cree admits. As long as there is buy-in from the head and managers, he argues, this needn't matter. Parental lack of enthusiasm can even be reversed if children are won over: Forestry Commission research showed a ripple effect whereby youngsters encouraged their parents to venture outside.

Back in the woodland near Ashdon, close to the market town of Saffron Walden, a circle of two- to four-year-old pre-schoolers are sitting on logs around a small campfire, munching on fire-grilled toast. Even the smallest understands the need to walk around the outside of the log circle rather than cross near the flames, just as each can whittle sticks safely using a potato peeler or use loppers and secateurs to tackle larger branches.

It's easy to tell the children who have been outside regularly, according to forest school leader Sue Cowling: "They're willing to try anything and everything and they will work out for themselves how to risk take, whereas those that have been more sheltered want to hold your hand and be guided a bit more. But it doesn't take long for them to settle in and be more confident."

An Ofsted report last year pronounced the pre-school good, praising the "high levels of curiosity and imagination" and positive relationships shown by the children in their "unique setting", but withholding an outstanding rating on the basis that the children had too few opportunities to "turn on and operate information and communication and technology equipment".

With the birds singing and a tractor ploughing a neighbouring field, the comment seems almost wilfully to miss the point. Pluck, who is Danish and herself enjoyed a largely outdoor early education, says: "We can teach anything here: we practise writing in the mud with sticks, we count stones in the stream, we learn the names of the trees and recognise their leaves.

"Children start school so young in this country: they would get much more from being outside and socialising, improving their language and physical development. It was cold recently and a little boy here was swinging his arms: he told me: 'Lili, when it's a bit cold you have to keep moving'. Then he pointed out the berries on the trees. If you can do all that at his age, you will be all right in your life."

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