The headteacher of another city academy has quit, the fifth to stand down in just 12 months.
Eddie Brady's departure from the Unity city academy in Middlesbrough has led to renewed concern over the pressure on heads.
The majority of England's 12 academies have been open for just over a year but have already suffered serious setbacks. Greig city academy in London's Haringey is in the hands of its third principal, and the heads of the Capital city academy, Brent, and the Kings academy, also in Middlesbrough, have quit in the past year.
Most principals are headhunted for the posts and are tempted by six-figure salaries. But with academies at the heart of Labour's plans to revamp secondary education, there is huge pressure to deliver quick results.
Mr Brady is believed to have been asked to resign following a difficult first two years for the pound;18 million Unity city academy, which is backed by Amey plc, the building and support services group. The academy, created following the closure of the struggling Keldholme and Langbaurgh schools, was criticised after expelling 18 pupils in 2002-3 and 14 last year. Results have been slow to improve and last year 17.6 per cent of pupils left with five good GCSEs.
Rita Harris, secretary of Middlesbrough National Union of Teachers' branch, said relationships between teachers and senior figures at the school were frosty. "Some staff felt they were not getting the backing they needed in dealing with some pupils," she said. "The other issue was that staff had to accept different terms and conditions and the working day has been altered - many were not happy with that."
Mr Brady reached agreement with the school to leave earlier this month. The deal prevents him discussing his departure publicly.
Lesley Humphries, deputy head, is now in temporary charge. In a statement, the school said: "Eddie Brady has decided to leave the Unity city academy.
Eddie became principal of the academy at its inception two years ago.
Having successfully led the school to a point at which it is firmly established in its new building, he has decided that this would be an opportune time to move on."
The Government has pledged to open 200 new academies, privately-sponsored schools independent of local councils, by 2010.
But John Dunford, general secretary of the Secondary Heads Association, said heads had to be given more time and support. "It is a high-risk, high-paid job. These people have been very successful heads of schools but many are just unable to hold down an academy headship," he said.
"The governors and sponsors have to realise that turning around these very difficult schools is not an overnight job, but some people just want instant success.
"I'm not saying expectations should be lowered, but heads must be given more time to reach those goals and support structures have to be improved."
The Greig city academy has had the highest turnover of heads.
Graham Horsewood quit last year after inspectors criticised teaching standards and pupil behaviour. Frank Thomas left the Capital city academy in July for personal reasons, insisting his departure was unrelated to a move to make seven staff redundant. And Richard Coupe, the original head of the Kings academy, was demoted to vice-principal before walking out last year.