Retirements among primary heads are almost twice as likely to be the result of ill-health than their secondary colleagues, official figures suggest.
Of the 2,570 nursery and primary heads who retired in the three years up to March 2002, about one in four, or 650 people, left on ill-health grounds.
This compared to 100 of the 700 secondary heads who retired in the same period.
Ill-health also claimed a quarter of the 21,540 teachers who retired from both sectors in the three years, according to the figures which are the most recent available.
About half of those who retired sick were suffering mental health problems, according to government research. Unions would like to see the stress of teaching relieved earlier in teachers' careers.
Six councils have been piloting a mix of prevention and early intervention measures to reduce ill-health retirements.
Mike Beard, assistant secretary (pensions) of the National Association of Head Teachers, said: "Some authorities have managed to lower applications going forward for ill-health retirement."
In primary schools, heads may have to combine teaching and management duties.
Mike Carter, chairman of the National Small Schools Forum, said: "Although being head of a small school is one of the most rewarding jobs in education, it is also one of the most demanding. Quite a number of heads do leave for stress-related reasons."
Secondary heads are the most likely of all teaching staff to be granted premature retirement, with 46 per cent of those retiring going on a full pension in 20012 compared to a third of primary heads and less than a fifth of teachers.
The figures also showed that around one in five secondary heads retired over the three years compared with one in eight primary heads. Martin Ward, deputy general secretary of the Secondary Heads Association, said:
"Councils seeking to get rid of a headteacher before or during an inspection is more common in secondary than primary.
"My experience is that headteachers resist retiring through ill-health. In practice it is taken only by people who are desperately ill and really can't continue. Others, who might have a claim, generally prefer to struggle on.
"It is not a question of whether the role of a primary or secondary head is more stressful. They are both demanding in different ways."
Figures this week from a survey by the School Teachers' Review Body show that the total average weekly hours worked by secondary classroom teachers is 50.8 hours and primary classroom teachers 51.8. Primary heads' weekly average was 55.5 hours and secondary heads 60.9.