Teachers' mental health problems are more likely to be caused by stress at home than at school, according to new research.
Workplace stress is to blame for fewer than half of the "alarmingly high" number of teachers who retire because of mental illness, a study by academics at Cambridge and Oxford universities found.
They will present their findings at the British Educational Research Association conference in Edinburgh tomorrow.
More than 2,300 of the country's half a million teachers left the profession as a result of sickness in 2002, official figures show. About half of these retirements were caused by mental health problems.
The study compared the stress suffered by 52 teachers who retired as a result of clinical depression with 52 staff who escaped mental health problems Research carried out for the Department for Education and Skills in 2000 showed that more than half of staff who retire ill believe work contributed to their condition. One in 10 said they had been bullied by a manager or colleague.
The profession's complaints are reflected in the high premiums demanded by insurance companies from teachers who buy income protection policies.
These rate teaching as nearly as dangerous as firefighting, policing or a career in the army.
The average 30-year-old non-smoking male teacher pays pound;64 in premiums every month for income protection insurance worth pound;20,000-a-year.
That is the same as investment bankers, sales managers and surgeons, and more than for working in an office, as a civil servant or secretary.
"Teachers are charged more than they might expect," said Simon Gadd, protection products director at Legal and General. "They tend to think of themselves in the same category as office workers and administration staff.
"But teaching is a higher risk because of the stress levels, and insurance companies know from experience that they have made a lot of claims in the past."
However, the National Union of Teachers is not convinced. A spokesman said:
"It's difficult to understand how the insurance industry can justify charging teachers extra just because of a perceived greater vulnerability to stress-related illness.
"There is a high level of stress in teaching, but it doesn't always lead to inability to work, as Government figures show."
The good news for teachers is that insurance companies may soon be forced to start reducing their premiums because ill-health retirement in the profession has more than halved since 1997 when the total reached 4,980.
'The role of school stress in the precipitation of severe mental breakdown in teachers' by C M Hargate and A D O Ogilvie. More details at www.bera.ac.uk