Inspections by the education watchdog Ofsted have harmed schools more than any other education reform in the past decade, a study of primary school teachers in England suggests.

Even the number of examinations pupils in England now have to sit were seen as less damaging, according to the findings.

Teachers questioned as part of the study, conducted by two Cambridge University professors, said the inspections damaged working conditions and "pupil opportunity".

Ofsted has always acknowledged inspection can be stressful and has taken many steps to reduce that stress

Ofsted

The introduction of the maths hour and the national curriculum in the 1990s were believed to be the most beneficial reforms of recent times.

A total of 267 primary teachers were interview as part of the study.

On a scale of one to five, where one is the most harmful, Ofsted inspections score 1.7.

But the education watchdog denies they are bad for children.

"External inspection has been one of the key contributors to the rising standards in English schools," a spokesman said.

"It has introduced accountability and enabled parents to find out more about their children's education.

"Ofsted has always acknowledged inspection can be stressful and has taken many steps to reduce that stress.

'Extreme pressure'

"But, for most teachers, inspection happens for just one week every four or five years, so it is difficult to see how this adds significantly to their regular workload."

However, the general secretary of the National Union of Teachers, Doug McAvoy, said the study showed teachers were under "extreme pressure over which they have no control or influence".

Schools could be devastated by failing inspections or missing targets, he added.

The second most damaging reform is compulsory national tests for seven and 11-year-olds, followed by performance assessment, according to the report.

Professor Maurice Galton and Professor John MacBeath also found teachers were worried that the emphasis put on reading, writing and arithmetic was pushing other subjects, including art and music, off the timetable.