Pupils are more likely to get better results if their teacher is new to the profession. Research reveals that 80 per cent of staff in their first seven years in the classroom produced value-added results at or above the expected level. But this fell to 68 per cent for those with between eight and 23 years' experience and to 59 per cent for those with 24 years or more.
The researchers suggested experienced teachers gave poorer added value because they have more complicated domestic lives, greater professional responsibilities, more health problems, plus the possibility that they are often overlooked for training.
John Bangs, the National Union of Teachers' head of education, said:
"Experienced teachers are neglected shamefully for professional development."
He and other teacher unions suggested that experienced staff may be given the toughest classes to teach. But the study takes this into account and rules out other possible contributory factors such as prior pupil attainment and their social background.
The four-year study into teachers' lives by Nottingham university and London university's Institute of Education used a nationally representative sample of 300 primary and secondary English and maths teachers between 2001 and 2005 and analysed pupils' test results.
Professor Christopher Day, who led the study, said: "This was a surprise to us. Until now it was thought that when you enter teaching you are a novice and you move through stages until you become an expert.
"This rather explodes that theory because it means that teachers do not necessarily translate that experience into pupil attainment. But it doesn't mean these teachers are not effective in other ways, such as the pastoral care they offer their pupils."
One third of teachers in England have had more than 24 years in the classroom, the category least likely to "break the mould" with better than expected exam results, according to the study.
The research also found that the more deprived pupils a school has, the sicker its teachers are likely to be. Problems attributed to the job included high blood pressure, multiple sclerosis, stress and depression.
The findings have prompted calls for the Government, which sponsored the research, to do more to provide support for those working in the toughest schools and those approaching the end of their careers.
It found that individual teachers made far more of a contribution to test results than expected: they accounted for between 15 to 30 per cent of the variation between pupils. Schools, it judged, account for only between 5 and 10 per cent of the difference.
Overall, a quarter of teachers were "breaking the mould" - their pupils were doing better than predicted - while the performance of more than half was in line with expectations.
Matthew Barton, 25, a geography teacher at Dowdales school, Dalton-in-Furness and winner of the North-east and Cumbria regional award of the outstanding new teacher award, said: "Generally younger teachers come in with new and fresher ideas, with all the new methods they teach trainees. We're probably a bit more approachable, too."
But Rachel Beck, 32, from Edgworth primary, Bolton, winner of the outstanding new teacher in the North-west, said: "I've learnt everything I know from my older, more experienced colleagues who have really inspired me."
full reports, p45