Headteachers are being forced out of their jobs due to "unrealistic expectations" and intense pressures to improve schools quickly, it has been suggested.
School leaders are falling victim to a "football manager syndrome" which sees them booted out of their role on the basis of one year's exam results or a critical Ofsted inspection, according to Brian Lightman, general secretary of the Association of School and College Leaders (ASCL).
In the autumn of last year alone, the union supported almost 150 school leaders, including heads, deputies and assistant heads, out of their roles, he said.
The situation is also putting people off becoming school leaders, for fear that they may find themselves jobless, Mr Lightman added.
In his speech to ASCL's annual conference in Birmingham, Mr Lightman said a poll for the union had found that 78% of members were less likely to seek posts in challenging schools than they were a year ago.
"Can you blame them?" he said.
"The accountability system has a lot to answer for in this respect. We continue to see schools dropping into Ofsted categories on the basis of one year's examination results, unrealistic expectations of the time it takes to improve and an intensification of the football manager syndrome which destroys careers.
"It is no wonder that school leaders think twice when they see these scandalous statistics. It is a disgraceful waste of professional capital."
Mr Lightman told the conference that between September and December last year, ASCL had supported 146 school leaders out of their jobs, of these 67 were headteachers.
"Headship is not a one-year job," he said.
"It is a long haul. Or to misquote Oscar Wilde: 'To lose one headteacher may be regarded as a misfortune; to lose hundreds looks like carelessness'."
Speaking ahead of the conference, Mr Lightman said that the union thinks that the numbers being forced out of posts is increasing.
"It's very difficult to tell over a period because obviously that's a snapshot within a four-month period, but it certainly looks that if it carries on like that, it's looking higher.
"And what we're seeing, the feedback we're getting from our member support teams, is that not only are they getting more cases of this sort of situation, often quite rapidly reacting to something like an Ofsted inspection, not necessarily bringing a school into a formal category of special measures but just an inspection that was critical somehow."
He added that many individuals are now reluctant to go for top jobs.
"They're thinking 'if I go for that top job in a challenging school' - which is what the Government wants and what we're trying to help them with - 'will I, if I've got a mortgage and financial commitments, going to end up without a job?'"
In a question and answer session at the conference yesterday, Education Secretary Michael Gove said that he did not want good school leaders to be put off working in challenging schools, saying that none of the things that the Government wants to achieve can be done if "good people that can make a demonstrable difference to schools going through a bad time are dissuaded from going for it".