Eggs come from cows,” declares eight-year-old Sabella confidently, in response to an inquiry about where food comes from. “And bread comes out of plastic bags in supermarkets,” chips in his classmate, nine-year-old Wayne, perhaps with a certain irony.

The question has been posed by Ali Stevenson, education officer at Pimhill Farm, near Shrewsbury, one of a dozen organic farms in the UK now offering school visits and education tours. Twenty more such farms will be joining a special educational farms network supported by the Soil Assocation during next year.

Here at Pimhill, Ali is used to young visitors thinking that cheese grows on shelves in Tesco and wool comes from Woolworth’s. Her experience is born out by a recent Mori survey (commissioned by the National Farmers Union) which identified real gaps in children’s basic understanding of the food they eat and how it is produced.

Today it’s the turn of class 4H from Welford primary school in Handsworth, inner-city Birmingham, to try out the farm’s special nature trail with activities linked to geography and science.

The first organic animal the children encounter is a pig called Jenny. Being a Gloucester Old Spot, she’s a large specimen and squeals loudly. Some of her young audience squeal even louder. Most of these pupils have never seen a pig close up and certainly not one this big. They move on past goats, donkeys and Blossom the old shire horse, to a panoramic view of the English countryside.

Abruptly the fields give way to a long rolling hill edged by woods and a church spire in the distance. “It’s ragged, man,” shouts Kieran as he charges off down the slope, to be followed by the rest of the group.

The vista also reveals the farm’s crop rotation system, an important aspect of organic farming. Rotation, explains Ali, helps to provide essential nutrients, reduce weed and pest problems, and maintain soil structure.

Once everyone has caught their breath again, they disappear through a shady wood before emerging into another field lower down in the valley. Suddenly the children fall silent. A herd of Jersey cows is grazing. The size of their milk-laden udders inspires a moment of hushed amazement. Then the penny drops for someone. “So that’s where milk comes from,” says Bushra pointing at Daisy, one of the larger members of the herd.

The education trail ends in a lofty 17th-century threshing barn criss-crossed by huge oak beams and flights of sparrows. Here Ali produces activity sheets and takes the class through the process of making wholemeal bread.

The group have already walked through a field of wheat on the farm trail and learnt about the different parts of the wheat’s ear and how it grows. Now they see it being ground by a traditional millstone into flour.

Next, the children explore the farm’s organic shop in search of mouth-watering bread, freshly baked in the farm’s kitchen, and other items made with flour. Pimhill is unusual even by organic farm standards in offering visitors the opportunity to see the whole cycle in one location and then taste the organic end product in its own shop and cafe.

The farm is run by third-generation organic farmer Ginny Mayall. “The children arrive expecting a bluff, red-cheeked farmer in braces with a walking staff and sheep-dog. Instead they find a young woman and a shop and cafe as well as the farm.”

She passes round slices of homebaked stone-ground loaves for Class 4H to taste. Not everyone is convinced of the merits of organic brown compared with their favourite white sliced. But by the end of the tour the majority of pupils are volunteering opinions about food, farming, health and the environment.

Says Mandeep: “It’s about growing things that are good for us and not spraying them.” Naomi has even stronger opinions: “It’s better than using chemicals which make us sick.”

The children are not simply parroting what they have heard from Ali on the farm trail but recalling, and now making more sense of, what they have already heard at home, on TV and in school. As an educational experience the day works well and complements an earlier visit to a conventional farm as part of their contrasting locality geography curriculum work.

Ginny Mayall says: “We work on the premise that children remember 80 per cent of what they do but 20 per cent of what they’re told. Visiting an organic farm is a great way of learning about the links between food and farming and how to take care of the countryside.”

Pimhill Farm, Harmer Hill, Shrewsbury SY4 3DY. Tel: 01939 290342. Pimhill is part of the Soil Assocation’s new Organic Farms Network. For information about organic farms welcoming school visits write to: Rupert Aker, the Soil Assocation, Bristol House, 40-56 Victoria Street, Bristol B51 6BH