All science teachers know that practical work does not always go to plan. Nature sometimes refuses to play ball - especially in school science labs. Consequently, neither do teachers and pupils. Pupils ask: “What’s really meant to happen?” and either manipulate nature, cross out their original, “wrong” prediction, or (in the top sets) keep it, so they can really go to town and score high marks on their evaluation.

For example, you connect seemingly identical bulbs in series but one is dimmer than another; you burn magnesium in air and there is no gain in mass; the starch test on leaves is inconclusive; you demonstrate the production of oxygen by photosynthesis of pond weed, but there is too little gas to do the oxygen test.

Over the past couple of years, with Mick Nott of Sheffield Hallam University, I have been exploring teachers’ attitudes to these scenarios - or “critical incidents” as we call them. Up and down the country, experienced and novice teachers respond to such results in one of three ways, depending on factors such as the time of day, their mood, or the type of class they are teaching. Some will talk their way through it. They discuss with pupils what “went wrong” and how the “experiment” could be improved. (Significantly, teachers and pupils seem to call all practical work in schools “experiments”.) Others resort to rigging - carefully adjusting the variables to achieve the “correct result”. But while many may do little more than, say, help demonstrations of photosynthesis (by doping the water with sodium bicarbonate or using growlights), a surprising number of teachers resort to what can only be described as fraud - for instance, surreptitiously bubbling in oxygen from a tank so the oxygen test appears to work.

Although few teachers could claim never to have used some sleight-of-hand, such behaviour runs counter to accepted standards of scientific behaviour. But how widespread is it, why is it done and when does it start?

A series of questionnaires and interviews confirmed anecdotal evidence on the widespread nature of such trickery in the United Kingdom. And we are now linking up with science educators in Australia, Canada and New Zealand to find out if and how it happens elsewhere.

But the more interesting aspect is why does it happen and when does it begin? Those who do conjure are remarkably articulate in justifying why they do it. A common reason is to avoid confusion: “It’s better the child understands the concept than get confused with an experiment that goes wrong,” said one teacher.

Another said: “It’s a compromise. You’ve got to weigh up whether what the pupils can learn from the practical is more important than you being straight with them, or them understanding the fallibility of science.”

There were many other comments of this kind. But one of the main justifications for conjuring in the current era of the national curriculum and public accountability involved the pressure to get results. “You are judged on one thing - pupils’ marks.” And: “At the end of the day, pupils want the answers to the exam questions The only way you can keep their motivation is to give them the answers they want.”

One novice teacher said the pressure to conjure filters down the department. “All teachers conjure - they have to, especially if you are following a scheme of work with set practicals.”

Conjuring seems to start surprisingly early in a teacher’s career, sometimes initiated by a mentor in teacher training but more commonly by an aiding and abetting lab technician. “Lab technicians say, ‘We’ve done this practical year in year out - it doesn’t work. Try conjuring it’.”

The ability to conjure during practical work is not yet a requirement of the new national curriculum for initial teacher training. So what (if anything) should we do about it? Is it unscientific behaviour? Those who express outrage are probably just hypocrites. How long has it been happening? Have the pressures of a state curriculum and league tables made it more common?

And what are the implications for the future of public understanding and faith in science? What damage has it done in the past? Were you aware of it when you were at school or were you unsuspecting, simply because you trusted the teacher’s integrity? As Benedict put it in Much Ado About Nothing: “I should think this a gull, ‘twere it not from the white bearded man.” It may happen in other subjects - or are there just lies, damned lies and science practicals?

* Readers’ reactions to all these questions would be most welcome. Comments please to j.wellington@sheffield.ac.uk

* Jerry Wellington is a reader in science education at Sheffield University. He has edited a collection of chapters entitled ‘Practical Work in Science: Which way Now?’ to be published later this year by Routledge

* REFERENCES: Nott M and Wellington J: Producing the Evidence, in ‘Research in Science Education’, Vol 27, No 3, 395-409