The osprey, the salmon and the dove watch over the Royal School of Dunkeld Primary from their vantage points atop a pine totem pole rising from the grassy playground.

Symbolising the school’s roots in the Perthshire landscape, the images are also a potent reminder of the wooded shores of the Pacific north-west, home to the craftsmen of the Squamish nation who visited the school to carve them.

“It was a week that stays in the memory,” says headteacher Sandy Howe. “The guys were wonderful with the kids. It was a real interchange of cultures; quite special.

“Since we started as an eco-school seven years ago we have made so many wonderful connections. A thread of serendipity winds through everything we do.”

Recently that thread has wound its way to a pink farmhouse in a barren landscape beneath a rocky ridge east of Pitlochry. All around the solitary stone building that Cameron and Moira Thomson have made their home, the wilderness of heather has been pushed back by a profusion of flowers and vegetable plots bulging with huge leeks, onions, turnips, cabbages, peas, beans, sprouts, lettuces, tomatoes and potatoes. It looks like magic or the product of some unnatural experiment but the truth is exactly the opposite.

Since last year, the Dunkeld pupils have been testing methods developed at the hill farm known as the Seer (sustainable ecological earth regeneration) Centre.

“We don’t use fertilisers or pesticides, just natural compost and rock dust from the Collace quarry. That’s what makes the difference,” says Mrs Thomson.

The theory is simple. Glaciers crush rocks during ice ages, creating soil with plenty of minerals and trace elements to sustain the world’s plant life during interglacial periods. It is now around 12,000 years since the last ice age glaciers receded and much of the mineral nourishment has been used up. Vegetation is having a hard time finding the variety of elements it needs for good health.

“Global average soil depth was 8ft then. Now it is 4.5in,” says Mr Thomson.

“The carbon that used to be in the deep soil and the giant trees is up there,” he gestures to the sky, “and the particles of stone have been washed to the sea.”

What the Seer Centre is doing, Mrs Thomson explains, is giving fertility treatment to the earth.

“Earthworms eat the rock dust and rotting vegetation and leave worm-casts that enrich the soil,” she says. “In clay soils worm-casts have no glitter because there are no stone particles. But look at this,” she picks up a dark brown pellet of soil, squeezes it between her finger and thumb and holds it out to the pupils. “Do you see how sparkly it is?” The children nod.

The decision to work with the Seer Centre and test the effects of rock dust in the school’s kitchen garden came from the pupils.

The national eco-schools award scheme encourages everyone in a school community to get involved in improving its environment. Mr Howe says: “The secret is to give the kids genuine responsibility. I’m constantly surprised by how well they exercise their judgment.”

P7 pupil Stephanie explains the project. “As well as growing things to eat, we have been doing experiments, growing exactly the same vegetables in each of the six beds. We put rock dust on one, manure on another, just soil on another. When we harvest the vegetables, we weigh them and find out what has worked best.”

Other gardens at the school include a den with building materials for play, a butterfly garden with lavender, buddleia and other plants chosen for their insect appeal, and a quiet, wild place with a pond that attracts newts, frogs and dragonflies (and Mr Howe, who often has lunch there).

All these features make a big difference to the pride and pleasure of being a pupil at an eco-school, says Emily, who used to attend a school without grass or gardens.

“If a school isn’t sure how to begin they could start small,” she says, “even with just one basket of flowers. The next year they could have two.

It doesn’t matter so much what you do, as long as you try.”

Grace believes persistence is the key to progress. “If you keep working on the things you want, eventually you will get them. Even if a school had all concrete, they could get boxes and grow flowers.”

Ideas can be borrowed from other schools, says Erica. “You can learn from what they do and they can learn from you.”

The sun beams on the front of the old school (which was founded in 1567 by the regent of the infant James VI), lighting up the autumn fire of the rowan trees. Near the totem pole is a circular clearing in the grass with rows of seats carved from tree trunks. “This outdoor classroom is another example of the nice things that happen at an eco-school,” says Mr Howe.

“There are occasions when the pupils take decisions I might not have done,” he says. “The principle has to be that you don’t ask children what they think if you aren’t going to listen to what they say. You have to be prepared to take that leap of faith in them.”

www.eco-schools.org.uk