Ray Richardson, Reader in Industrial Relations at the London School of Economics, says performance-related pay has rarely improved performance in the public sector and is unlikely to do so in schools.

And if higher pay does depend on pupils' results he warns of a "darker possibility": some teachers might be tempted to help children more than they should with course work, in an effort to boost the pupils' marks and hence their own salaries.

He predicts a "number of scandals" every year as a result.

Dr Richardson was asked by the National Union of Teachers (NUT) to investigate the pay proposals which ministers want to introduce in England. A similar scheme is proposed for teachers in Wales.

Appraisals

On Thursday the government is expected to make its submission about performance-related pay (PRP) to the teachers' pay review body for 2000, when the scheme is due to start.

Unions say linking pay to pupils' results is unreasonable

Under its proposals, teachers' annual pay rises would be linked to appraisals up to a new "threshold" of about £23,000.

Those who volunteer to rise above the threshold - and are judged to be good enough - would get an immediate rise of up to 10%, followed by annual increases which could take their salaries up to £35,000, subject to satisfactory appraisals.

The NUT is boycotting the new appraisals, currently being piloted in a number of schools.

'No major improvement'

Dr Richardson concludes that PRP has succeeded in stimulating productivity in private industry, particularly the manufacturing and financial sectors.

Studies have shown less success in the public sector, where it is harder to measure an individual worker's contribution.

But in the Inland Revenue, local government and the National Health Service there has been no major improvement in performance, with staff at best producing more in quantity rather than better quality.

And he says there has been a widespread perception that new pay systems have been unfair and divisive, with a negative impact on team-working and co-operation.

In surveys of employees, "rarely do more than 20% agree that it has given them an incentive to change ... their behaviour at work," Dr Richardson says.

'Roulette wheel'

He is critical of the way the government imagines the performance linking would work. Overall the criteria for judging performance are too complex, he says.

The exception is the link with exam results - the aspect most criticised by teachers as being unfair. They will regard it as "yet another turn of the ... roulette wheel", he says.

The other big fear is that the awarding of higher pay will in practice have more to do with the amount available in a school's budget than the performance of its teachers.

Dr Richardson says it might be that any salary increases for some staff would be paid for by lower rises for others.

"There must be a suspicion that the government is really using PRP for a somewhat different purpose than merely recruitment, retention and motivation," Dr Richardson says.

'Device'

"It is possible that the new proposals are really a way of rewarding a selective minority of teachers without incurring the wage bill costs of extending benefits across the board.

Older staff are said to be at risk

"It may be a device to attract ... a number of relatively high quality teachers while doing rather little for the large number of average performers."

But he says that teachers persuaded to remain in the profession higher, performance-related pay rises could be balanced by those leaving because they are denied a rise.

This chimes with a submission to the pay review body made on Tuesday by another union, the Professional Association of Teachers.

It argued that experienced teachers were being made redundant so that schools could balance budgets based on average not actual teacher salary costs.

"We are also finding that, under current funding arrangements, schools are employing younger, less experienced teachers because they are paid less than older, more experienced teachers - although even they are in short supply because of the recruitment crisis," it said.

'Dangers exposed'

The NUT's General Secretary, Doug McAvoy, said this was the sort of research the government should have carried out before it had published its proposals.

"Ministers need to examine this research in detail because it exposes the dangers of PRP which the government has not taken into account," he said.

But a senior government spokesman said its proposals had been developed in co-operation with teachers and heads.

"They are being fully trialled in schools at present. The system will be both fair and non-bureaucratic in its operation. We believe we have now got the balance right."