Research has found that 80 per cent of teachers in their first seven years in the classroom produced value-added results at or above the expected level. 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 four-year study into teachers' lives, by Nottingham university and London university's institute of education, compared academic attainment and age among a sample of 300 primary and secondary English and maths teachers from England and Wales between 2001-5.
Professor Christopher Day, who led the study, said: "This was a surprise to us. Until now there has been a theory 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.
* Research also conducted by the body found that that the more deprived pupils a school has, the sicker its teachers are likely to be. Problems included high blood pressure, multiple sclerosis, stress and depression.