With the grace and delicacy of a ballerina, Angus arches and points a long, elegant leg and gently steps across the teacher’s hand. Then he takes another careful and exquisite step. Then another, and another, and another and another and another and another.

Angus the tarantula is just one of the creepy-crawlies living in Stuart Ball’s Year 6 classroom at Llantilio Pertholey primary in Abergavenny, where his companions include a scorpion, giant African land snails, hissing woodlice, millipedes and another tarantula too nasty to be allowed out of its box.

Angus, on the other hand, leads quite a sociable life. Recently, he had travelled to London for The TES Primary Science Teacher of the Year judging, where Stuart was selected national winner from a strong field of regional finalists. Holding the spider is almost a rite of passage at Llantilio Pertholey, for pupils and adults alike, and every visitor who does so gets a certificate.

Arachnophobia is one of Stuart’s interests, and his class is helping him with research into why people are afraid of spiders and what can be done to help them. The project is part of The Primary Teacher as a Scientist programme, run by Homerton College, Cambridge. His expertise in science (he has a BEd in biology) does not disqualify him from learning along with the children (“That’s what gives me a buzz”) or from taking them along with him on his own explorations. “If I take an interest in something, I tend to bring it into the class,” he says. Hence the pictures of fractals on the classroom wall, and the “plasma ball” on the shelf.

You can buy plasma balls in the shops. They’re glass balls with filaments of light generating from the centre and splaying out in all directions, but which move toward your hand when you place it on the glass. But what is the “plasma”? What attracts the light? “I haven’t got a clue about the physics of it, ” says Stuart. But he and the class are exploring it together. It doesn’t bother him that he doesn’t know the answers, and it doesn’t bother the pupils, either. They are happy to put forward hypotheses (“Maybe it’s attracted to the heat”), discuss them, try them out.

“I don’t look at them as 10 and 11-year-olds,” says Stuart, 32. “We talk about DNA and genetic engineering - these are all things they’re exposed to on TV. They all know what DNA is. They’ve seen Jurassic Park.” The class discusses what would happen if you swapped genes from a bee and a cow. Would you be able to get honey from cows? With this type of approach, even more difficult issues such as Aids and sex education can be discussed comfortably.

In such an atmosphere of scientific discovery, obviously Angus the spider is far more than a curiosity. Stuart was given his first classroom tarantula by a visiting lecturer, and it soon achieved cult status, impressing children from other schools and always appearing in class photographs; but first and foremost the spider is “a focal point of interest about living things”.

“I have heard the nature table referred to as ‘the table of death’ because everything on it is dead,” says Stuart, who literally brings science to life. The evidence is not only on the nature table but in the children’s project books. Last term they were studying electricity, and were asked to think about what things looked like, and then find out more about them. Each child’s book contained drawings labelled “This is what I think it looks like inside steel” and “This is what I think it looks like in a piece of plastic”. One child had drawn the atoms, closer together in the steel and further apart in the plastic. Others had taken a more abstract approach.

The children in Stuart’s class think hard before answering a question, and are prepared to risk making an informed guess.

Morgan, 11, explains that the molecules in metal are “joined up so the electrons can run through, but in plastic they’re looser”. And what about that plasma ball? Liquid, he says, is a bit looser than a solid, and plasma is “looser still - it goes all over the place”.

Fractals, suggests Jason, 11, “are things that go on and on and on”. You get them by “zooming into a little bit of that, then a little bit of that”. But what’s the point? He ponders for a minute. “To look what’s inside all the patterns.”

“Most of my work is trying to get children to do investigations,” says Stuart. He believes it’s important to let the children investigate before the teacher explains the facts, rather than to tell them the facts first, and then let them find out what they already know. “Why tell them that their heartbeat gets faster when they exercise, when they can run around the yard and see it?” Because so much science is counter-intuitive, children develop many logical misconceptions: clouds are alive because they move, people have red and blue blood, metal conducts electricity because the molecules are loose enough to let the electrons through. Once they have done the investigations, the children can look back and see where they were right and where they were wrong.

“Before you do anything, get them to talk about their ideas,” Stuart says. “There’s been a lot of research on teachers undoing a lot of the knowledge the children already have.”

Morgan particularly enjoyed the pulse-measuring experiment. “The heartbeat goes up when we exercise,” he says, “but we thought if we kept running it would level out.” His friend James explains why: “If it kept on going up it would explode.”

Scientific thinking pervades Stuart’s classroom, but goes beyond its walls as well; children have been using the Internet to try to contact experts with their questions. Even art has a scientific angle, with pupils making their own versions of Escher’s tessellated drawings or 3-D models of his unlikely buildings in which stairs go both up and down, or columns hold up the wrong wall. Even a history project on Thomas Crapper in the corner of the room, featuring a real toilet bowl overhung with loo seats designed and made by the children (the best being a grinning alligator), suggests the thinking of a biologist.

Stuart’s own work spills beyond the classroom walls as well. He is involved with the Association for Science Education’s national primary committee, an ASEKing’s College project on science investigations, a local authority team developing curriculum materials, and the Nuffield Critical Maths Group, which is examining the place of science in the National Grid. Now he will be an ambassador for primary science as Primary Science Teacher of the Year.

Meanwhile, Angus the tarantula’s hectic lifestyle seems to have taken its toll, and he has developed a bald spot on his back. Perhaps it was the trauma of the trip to London. Or is it the noise in the classroom which has stressed him out? Or is he simply about to shed his skin? Stuart and his class will be finding out together. For primary science it will be another step forward - or eight.

TARANTULAS: FACT AND FICTION

* True tarantulas are small, poisonous spiders found in southern Europe, not hairy giants from South America * The tarantula gets its name from the the Italian town of Taranto. Tarantism, a “madness” believed to be caused by the spider’s bite, was widespread in southern Italy from the 15th to the 17th century * The South American spiders do not spin webs, but construct flat “arenas” outside the burrows of their prey * Tarantula fangs are the same size and sharpness as a cat’s claw * Female tarantulas can live into their late twenties. Males live only seven or eight years * There is no record of anyone dying from the venom of a pet tarantula * Little Miss Muffet was the daughter of Thomas Muffet, a 16th-century doctor who used live spiders to treat colds * The venom is about as potent as a bee’s sting. Most of the pain comes from the puncture holes left by the fangs Sources: Rachel Jones, invertebrate keeper, London Zoo Jason Curtis, Class 7, Llantilio Pertholey Primary