Wearing green safety tunics, cycle helmets and wellies, a dozen Year 6 children come hurtling down the winding woodland path on mountain bikes. Suddenly the woods end and they find themselves on the undulating sand dunes of Barafundle Bay. It is a tiny jewel of a beach tucked into the cliffs of south Pembrokeshire, a short bike ride from the National Trust's Stackpole for Schools education centre.
Despite Barafundle Bay's reputation as one of Britain's finest beaches, the high tides of the Bristol Channel wash up a line of rubbish amid the seaweed and spume. The pupils from Cogan Primary School in Penarth, South Wales are going to do a beach clean-up, and at the same time have a valuable lesson in sustainability and the natural environment.
Equipped with protective gloves and tongs, they collect anything non-biodegradable. They find plastic bottles, bits of old fisherman's net, crisp bags, an old Thermos flask, part of a deck chair, a CD case and the remains of an angler's plastic box.
With everything they pick up, National Trust education officer Dan Beck is on hand to explain what it is and how it got there. He finds a small blue rod of plastic lying in the sand. "Does anyone know what this is?" The children shake their heads. It's the remains of a cotton bud. He explains that thousands of these get washed up on our shores after people flush them down the loo without thinking. And judging from the looks of disgust on children's faces, the message is getting through. After collecting half-a-dozen sacks of litter, the pupils go off to dig in the sand.
Teacher Emma Evans says this hands-on lesson on the environment has been a good supplement to the children's classroom work. "It's making it real, not just some tenuous link in the curriculum," she says.
Stackpole for Schools opened in 1984 as the National Trust's first residential education centre. It is set in the Cawdor estate, 2,500 acres of unspoilt hilly woodland, fresh water lakes, limestone cliffs and beaches. The centre caters for week-long visits by primary and secondary schools and can take up to 45 children at a time. As well as offering a range of outdoor activities including rock climbing, abseiling and sea canoeing, its programmes aim to address environmental and sustainability issues.
Children get around the estate on the centre's fleet of mountain bikes.
They learn about recycling, but also get to practise it during their stay by conserving plastic, glass, paper and cans, and composting vegetable waste in the gardens. Messages and information about the environment cover the walls of the centre's common room, while the waste bins carry the warning "Whatever goes in here goes to a toxic landfill site".
There's also an emphasis on responsibility and self-reliance. Pupils have to make sure they turn off taps and lights, keep their own rooms in order and clean up to leave their accommodation just as they found it.
The stunning natural environment offers ample opportunity to see nature close-up. There's a bird hide and children go on woodland walks or explore rock pools with National Trust education officers. "There are plenty of outdoor activity places around, but where we are slightly different is that we have this environmental bias," says the centre's manager Gez Richards.
"We lay it down at the beginning of the week about waste and energy use. We monitor electricity use during the week and we talk about where waste goes.
When you put your bin out, not many kids know what happens to it. Then we try and reduce our waste. Most weeks we aim for the kids to produce just one bin bag of rubbish. That's quite good for 30 to 40 kids."
Cogan Primary School has organised trips to Stackpole for 15 years. The school runs an eco-club for its children, encouraging them to recycle paper and cans and conserve electricity and water. Head teacher Anne Bowsher says a stay at the centre offers valuable links with the curriculum, particularly with citizenship and personal, social and health education.
"It stimulates their interest in the world around them - it's first-hand experience," she says. "The first afternoon we all went on a woodland walk.
The instructors pointed out a type of lichen that won't grow unless there's a certain air purity. We looked at different fungi and saw various animal tracks. They would then talk about that animal and food chains."
But will the messages stay with them? "Very much so - more than they would in the classroom. Much more, because they are living the experience."
* Sustainable development and the environment
* Social responsibility
* The value of voluntary work Skills
* Discussion and debate
* Taking part in community activities
* Thinking about social issues
Stackpole for Schools. The Old Home, Farmyard, Stackpole, Pembroke SA71 5DQ. Tel 01646 661464. Opening times: Centre open from the beginning of February until the end of November.
Contact the centre for further information on availability.