If you put one ice cube on a cold block and another ice cube on a warm block, which will melt first?

TWO small black squares sit on the bench top, looking like stylish coasters.

One feels cold to the touch. The other feels warm, in that uncomfortable way a Styrofoam cup feels warm.

Sitting next to them is a large bucket of ice cubes.

Question, says Andrea Mapplebeck. If you put an ice cube on each of those squares, which one will melt first?

Well, it's obvious, isn't it? The warm square will melt the ice cube more quickly than the cold square.

Except... it doesn't. We watch, enthralled, as the ice cube on the "cold" square rapidly melts into a puddle while the ice cube on the "warm" square doesn't melt at all.

For a breathless moment, the laws of physics seem to have been turned on their heads.

"That's brilliant!" chortles Ken Longden, the larger-than-life head of science at Middlefield School Of Technology, in Gainsborough.

We're on a training course at York's brand new National Science Learning Centre, opened recently by Tony Blair.

Based at the University of York, it is the hub of a £50 million national network of centres which aims to improve the quality of science teaching across the country.

The course I've joined is for head teachers and aspiring heads of school science departments.

And what we've just seen is a simple but stunning demonstration of the principle of conductivity.

Some materials allow heat to pass easily from an area of higher heat to an area of lower heat.

Other materials, non-conductive or insulating ones, stop that transfer of heat.

"So why does one ice cube melt more quickly?" asks Andrea, a former science teacher at Lowfield School, in York, who is now a professional development leader at the science learning centre.

I stumble towards an explanation. The cold block only feels cold in relation to my hand, I say. Compared to the ice cube, it is warm.

The "warm" block, meanwhile, because it is insulating material, takes on the same temperature as the material it comes into contact with, so it feels warm to the touch.

Close but wrong, Andrea says. Actually, both blocks are the same temperature - room temperature, which is colder than my hand, but warmer than the ice cubes.

The cold one feels cold because it is conductive, so warmth flows from my hand to the block, making my hand feel cold.

But it is actually warmer than the ice cube, so warmth flows from the block into the ice, melting it.

The other block doesn't conduct heat. No warmth flows out of my hand into it, so my hand doesn't feel cold when I touch it, making me think it is warm. But if you put an ice cube on it, no warmth flows from the block to the ice either, so it doesn't melt.

All my colleagues, being science teachers, knew that already.

What is brilliant about the experiment, says Ken, is the "wow factor".

Imagine an 11-year-old being asked to touch those blocks, then predict which will melt ice the quickest. They will be astonished, and they will want to do it again, and then they will want to explain why it happened.

That is what great science teaching is all about. Getting students to think for themselves about why things happen, and then try to come up with explanations.

We try our hands at several different experiments, all designed to stimulate thinking.

We roll little metal balls along a track studded with magnets, and have to try to explain why they pick up speed (great fun because, by the end, the balls are going like a rocket).

We try to work out why juice from fresh pineapples stops jelly setting, while juice from boiled pineapples doesn't (it is all to do with the enzymes in pineapple).

And we watch a group of woodlice in a dish, and have to explain why they all try to climb on top of each other, like rugby players in a scrum.

I remember my A-level biology classes.

"Woodlice have porous skin which means they dry out very quickly in bright light," I say.

That's why they live under stones and in dark, damp places.

If they huddle together like that when out in the light, they reduce the area of skin they each have exposed to the air, so they dry out less quickly (a bit like penguins huddling together at the south pole to reduce the area of skin exposed to the cold, so that they lose heat less quickly).

"Okay," says Andrea. "Now think of how you would prove that theory."

"Put groups of woodlice in different conditions," suggests Ken - bright and dry, bright and damp, dark and dry, dark and damp - "And see if that affects their behaviour?"

At the end, we all come together to share our experiences of the experiments, and to discuss the best ways of using them in class.

It makes for a stimulating and lively discussion, in which scientific theories, ingenious experiments, and ideas for getting kids involved, are tossed back and forth.

That is one of the most valuable parts of the whole experience, says Deborah Gogliormella, an assistant head of science at Thornton Grammar School, in Bradford.

"It is really rewarding," she says. "You get the chance to network with other teachers in the same position as yourselves. I've got lots of ideas, and I'll be able to go back to school feeling fresher and a bit more motivated."

A thousand senior science teachers from all over the country are due to attend courses at this centre over the next year. If they all go back to school feeling the same, science teaching in this country could be about to get a lot better.

No expense has been spared at the lavish new National Science Learning Centre.

There are state-of-the-art teaching labs, an ICT suite where teachers can create their own multi-media teaching material, and a resource centre - open to science teachers in York - stuffed with all the latest educational tools, books, journals and gadgets.

There are seminar rooms, a 64-bed accommodation block for visiting teachers, a smart new restaurant, geothermal heating and a stunning domed central atrium and reception area.

It is all high quality and aspirational - as you would expect of a national centre.

Around the central atrium, there is a famous quote from Goethe: "Science and art belong to the whole world, and before them vanish the barriers of nationality."

In one of the corridors there is an even more famous quote, from Newton: "If I have seen further, it is by standing on the shoulders of giants."

The £25 million York centre - funded by the Wellcome Trust, and operated by the universities of York, Leeds, Sheffield and Sheffield Hallam - is just the hub of a wider national network of centres intended to drive up the quality of science teaching across the country.

There are nine regional centres in addition to the York base, which between them have cost another £26 million, paid for by the Department for Education and Skills.

It is great to have such a prestigious institution as this - a national centre of excellence for science teaching - right here on our doorstep.

But why was York chosen? And why do we suddenly need a national centre for improving the teaching of science now, when we seem to have been bumbling along for decades quite happily?

The centre's director is John Holman, a former school head teacher who is now professor of chemistry at the University of York.

The "why York?" question is simple, he says. York has a national reputation for excellence in science education and curriculum design, thanks to the university's science education group, which brings together the education department and working scientists.

It was the York group, for example, which drew up the blueprint for new science GCSEs which come into effect from September.

As to the "why now?" question: that's more complicated. Part of it is, in an increasingly science and technology-dominated age, ordinary people have to have a better understanding of science if they are to participate fully in society.

Every day, we are confronted with problems that involve science. Issues such as whether the MMR vaccine is safe, what we should do about global warming, or whether we can trust GM technology, all require us to understand the basic scientific principles involved if we are to play a meaningful part in the debate.

Not every schoolchild is going to grow up to become a scientist, says Anna Gawthorp, the centre's communications director. "But in a modern society, we do all have to understand science enough to be able to participate in society and enjoy life," she says.

So, it is important teachers teach science in a way that is interesting and exciting, so their pupils aren't switched off. And, because science moves on so fast, it is important they should be kept up-to-date with new science and teaching methods.

The quality of science teaching is particularly important, says Mr Holman, because too often science is perceived by children as "too difficult". That, if it goes unchecked, could easily lead to a generation of young people who are turned off by science.

There is some evidence already that a dislike of science may be ingrained in our culture. "It is possible for me to tell someone that I'm a scientist and for them to say 'I don't know any science'," Prof Holman says. "But if someone said to me 'I'm a novelist' and I said I had never read a word of Shakespeare - that's not acceptable."

The national centre, therefore, is about the future of science in this country.

"It will help the UK to nurture promising young minds and inspire them to become scientists," says Prof Holman.

"But it will also improve science teaching for all young people. The initiative is designed to inspire their teachers to teach them the most interesting, relevant and thought-provoking science, that will stay with them for the rest of their lives."