Can you use your imagination?" says the geology guide, to the group of 10-year-olds on their geography field trip. "I need you to close your eyes and cast your mind back 400 million years - to days when there were no exams and no homework."
With that and other trusted tricks, Eleri Jones has the 17 boys from Dulwich college hooked looking for fossils, identifying rocks and figuring out their uses.
The hour-long geology time trail started down by a stream, where Ms Jones invited the boys to select a pebble. And from the pebble's characteristics - shape, texture, colour and weight - the boys are introduced to the different rock types.
"Three hundred and eighty million years ago this area was like a desert,"
says the teacher turned education officer with the Brecon Beacons National Park.
"The sand from the desert was eroded away, washed down to the bottom of the stream and it made the red sandstone that lies beneath us."
Geology sounds so simple when explained like that. "Look boys," says Ms Jones. "The sand comes off when you rub it. It is so soft you can carve it into shapes." As they climb up the hill the boys build up an idea of the underlying geology and how it shaped the area around them.
"Each step represents one million years," continues Ms Jones. "Let's count 20 million years and see what we find." The group walk on excitedly, halting beside a paler coloured outcrop that they correctly identify as limestone. "Its fissures allow water to run through it," says Ms Jones. "It is used for whitewashing many of the houses in the area."
We are in the western end of the National Park, where Fforest Fawr (Great Forest) is promoting its new Unesco Geopark status - the fifth in the UK and a proud first for Wales.
The aim of the Geopark initiative, which dates from 1999, is to protect and promote unique geological sites to wider audiences through sustainable tourism and education.
Those in the UK (see below) are located within National Parks or Areas of Outstanding Natural Beauty - apart from Abberley and Malvern Hills. Here in the Brecon Beacons they have been running educational courses for years for schools from the Swansea valley to South London.
The courses link in particular into key stage two: geography, science, art and personal, social and health education. But spurred on by the new status, it is expanding into KS1, with a course on investigating woodland habitats.
As well as the geology time trail, Fforest Fawr also organises a geological fortnight for schools (with free local transport) and provides rock trails for investigating the area's historical cultural sites, such as the limestone that makes up Carreg Castle and the red cairn sandstone that surrounds Garn Goch Hill Fort.
You do not have to visit the Geoparks to profit from the diversity of what they have to offer. The North Pennines, for example, has 20 rock boxes it loans schools, with activities to go with them. And it provides field-based worksheets for visits to Upper Teesdale, whose arctic alpine flora is unique to England; or High Force, which is England's biggest waterfall; or the karst limestone scenery around God's Bridge.
From next September, Marble Arch Caves Geopark, in Northern Ireland, will be offering many of its activities through its website, which all link neatly into the curriculum. They include guided walks for KS1 upwards, which involve children imagining themselves as Fuzzy the Squirrel and going on a mini beast hunt, right up to role-playing a public inquiry on the future of the area's Blanket Bog.
In north-west Scotland things are most developed at Knockan Crag, 21km north of Ullapool, where worksheets, CD-Roms and an on-screen quiz can entertain schools visitors - with teachers' notes on the website.
The Geopark also runs courses for children to make fossils, learn about cave paintings or go panning for gold. Particularly popular has been an intriguing sounding "mountain experiment box", loaned by the British Geological Survey. You fill it up with different coloured soils, and the machine is then able to demonstrate what happens to rock layers under pressure from the earth's core.
"Geology is not an easy subject to teach," admits Helen Kahn, the accompanying teacher from Dulwich college. "But it is amazing what the children take in when they see it for themselves"
Abberley and Malvern Hills, WorcestershireShropshireGloucestershireHerefordshire www.worc.ac.uk
Fforest Fawr, Powys www.breconbeacons.org 01874 624437
Marble Arch Caves Cuilcagh Mountain Park, Fermanagh, Northern Ireland
www.marblearchcaves.net 02866 348855
North Pennines, Durham www.northpennines.org.uk 01388 528801
North West Highlands, Wester Ross and North West Sutherland, Scotland
www.northwest-highlands-geopark.org.uk 01571 844000