For the sixth-formers from Hewett school in Norwich, the highs and lows of Malham Tarn provide a very different landscape to the flatlands of home.

Set in the Yorkshire Dales, the tarn is the highest natural lake in England. It is a National Nature Reserve and a Site of Special Scientific Interest (SSSI) site with three different wetland habitats - open water, a fen and a raised bog. The magnificent spectacle that is Malham Cove, a limestone amphitheatre formed after the last ice age, is a short walk away, as is Gordale Scar, a huge gorge with near-vertical 100m sides. This is a classic upland limestone landscape - a geographer or biologist’s delight.

The group has arrived at the National Trust-owned site for five days of fieldwork. On the first afternoon pupils stretch their legs and finding out how this mysterious lake and its bog were formed. “The change does them good,” says class teacher Donna Reynolds. “As soon as we start going up the hills and down the dales it’s as if they’re in a foreign country.”

As the group walks across the bog on a sturdy man-made boardwalk, we hear barking and howling in the distance. The mist is rolling in yet everyone is surprisingly calm. Has none of these students read The Hound of the Baskervilles? On closer inspection, the dog turns out to be a small poodle with a curiously deep bark.

There are few people on the bog because special permits have to be obtained to gain access to the site. The boardwalk stretches across decomposing vegetation which is five metres deep.

“The tarn is now a third of its original size with a surface area of around 150 acres,” explains Jon Banner, a field studies tutor from Tarn House, where the group is staying. “The plants have been taking over, but that process has been halted by human interference - the building of a dam.”

(In 1791, the level of the Tarn was raised by approximately 1.2m (four feet) with the construction of the dam and weir at Tarn Foot by Lord Ribblesdale.) Jon gives us a fascinating picture of how the tarn began, and with the current maintenance hope it will remain intact for the future. Once off the boardwalk we walk on dark mud and springy turf, following a stream until we reach the area he has chosen for the field work. The students are in groups of three and are armed with data recording sheets, illustration sheets and half-metre quadrats.

All equipment has been provided by Tarn House and, in what seems like an instant, Jon Banner has organised the unfurling of five 30-metre tape measures. Each tape is laid at right angles to the stream.

Pupil Shanti Rudling and her two companions work at intervals along the length of their tape measure. They are recording what is growing in each square of their quadrant - a fascinating variety by the looks of things.

They have established a rhythm to their work, seemingly without thinking.

“Wow. I’ve never been anywhere quite like this before”, says Shanti, when she reaches the end of the tape.

On other days, they will be investigating river systems and walking to Malham to look at the effects of tourism.

On the final day, the students are given the opportunity to carry out further study at one of the previous locations.

“Choice gives them ownership and motivation,” explains geography teacher Tim Fromant. “Within a group of three students, each one could be looking at the bog from a different perspective. One might have a scientist’s perspective, another a biologist’s.”

During the trip, the group stayed at the hostel Tarn House, five minutes from Malham Tarn and overlooking a lake. It has good sleeping facilities for up to 85 students and teachers, an eating area and laboratoryclassroom facilities with projectors, computers with appropriate programmes and equipment for soil and water testing.