MENTION league tables to teachers and you won't see them jumping up and down with enthusiasm. The most you can hope for is a qualified agreement that we need some way of measuring a school's success.

Many teachers complain bitterly that their performance is graded so crudely. And it isn't easy to know which figures to trust, because there are many, many league tables. Which one is the best measure of success? Some schools excel at Key Stage 3, others in getting 5 A-C grades at GCSE.

Many schools score very highly on their total number of GCSE passes, but are much lower in tables which compare results for maths and English. This is usually because they have a large number of pupils taking GNVQs - a more practical qualification which suits less academic students. So are these schools deliberately blurring the picture by entering their pupils for easy exams? Or are they actually doing a great job, by making their students play to their strengths? It all depends how you want to look at it.

League tables can be downright misleading. A school with a very mixed intake in a more deprived area is not a failing school because its GCSE pass rate is lower than a selective grammar school. In fact, it could be doing a better job of bringing out the best in its pupils.

This is one of the reasons why many teachers prefer the catchy-named "Contextual Value Added" league tables. They try to assess pupils' potential as they enter a school. For secondary schools, they consider Key Stage 2 performance and take into account other relevant factors, like where children live. Based on this data, they try to predict what each pupil should realistically be capable of at GCSE. So, you should be able to see which schools help students achieve more than could be expected and which schools actually damage their chances of success.

Even this system has its flaws, however. My husband has a class of bright pupils, many of whom came from an excellent primary school where they all achieved high scores at Key Stage 2. Value-added criteria dictates that this class should therefore all score As or A*s at GCSE. In the league tables, he would look better if they had done worse at primary school. Then he could be seen to have "improved them" with his dazzling teaching.

How league tables affect teachers largely depends on the attitude of their school's management. Tim Kirkup, headmaster of the private school Scarborough College, takes a relaxed approach to the whole thing. "Once you're fixated on scores, you become part of the culture which teaches children to jump through hoops - practising assignments, retaking modules over and over, just teaching in order to pass exams. There's no longer any place for teaching things because you think they are valuable in their own right."

He is in an unusual position, however. "The spotlight is always on local state schools," he says. But this doesn't mean he is complacent about standards. Staff in his school have to account for their results from year to year. "When I had piano lessons as a boy, I only practised because I was scared of my teacher," he admits. "A certain amount of the right kind of fear can be helpful. But most people function best when they feel supported, secure and happy."

Does that mean it's more important to be happy than successful?

"Oh no," he insists. "That's far too cosy. It's important that teachers aren't always operating within their comfort zone. But, when teachers feel that you believe in them and are encouraged each time they succeed, they tend to go on and scale heights you thought impossible. Imposing point-scores and levels on teachers denies all that - it's ultimately rather dreary."

I can't help feeling that his staff are rather lucky: they seem to be operating outside the glare of public scrutiny which dogs most state schools. Many headteachers are thrown into an anxious frenzy by comparisons of their school to local or national standards. Schools which are under pressure, after a critical Ofsted report, or poor exam results, are more likely to pressurise their staff.

At one school I know, there is a new policy of publishing value-added scores for each class, so that teachers can see how they score compared to their colleagues. The results have been quite unpleasant. Staff tend to compete with each other, and many feel crushed by their apparent lack of success.

"People feel they are being rated as professionals according to this crude, numerical score," one teacher says. "And yet we all know that it's easier to get children to succeed in certain subjects. Put them in front of a computer, for example, and they all concentrate much better. The IT department seem to think they are all brilliant teachers because of their scores. Just let them try teaching maths last period on a Friday."

League tables create other pressures too. When I taught English in a top public school, I was expected to re-mark drafts of course work over and over again until they were perfect. That way, the boys scored top marks, but only because of my efforts. It felt dishonest, because the final course work said more about my dedication than the students' ability. I just didn't want to be the one teacher whose class let down the school in the league tables.

Similarly, it's now fairly standard practice for schools to focus extra attention on pupils who are borderline candidates - to get them up to a C at GCSE, or the next level in their SATs (Standard Assessment Tests). You could argue that this makes educational sense: we all know the importance of a C at GCSE. Or, you could say that it values some children more than others, simply because they are likely to improve the school's overall league table performance.

Children do notice what we are doing to them. More than once, I have heard students comment that they are valued more for their results than who they are. One boy in my husband's class, tired of being drilled to pass exams, complained: "You're training us to be performing dogs."

So is it all bad? I don't think so. Most teachers' attitude to league tables says more about the approach of their school's management team than it does about the statistics themselves.

It's also important to remember that league tables are only one measure of a school's success. Maybe what we need now is a league table of happiness and self-esteem - for teachers and pupils.

Hilary Cooper is a general studies teacher at Queen Elizabeth Sixth Form College, Darlington.

For a full round up of the league tables see page 38