School reforms may cause more than two thirds of secondary school headteachers to leave the profession, according to a survey.
Ministers' attitudes to teaching has made 67.9% of school leaders more likely to leave the profession in the next five years.
Additionally, three out of five headteachers believe children's education will be damaged by the government's school reforms, the questionnaire also suggests.
The poll of 1,800 heads, conducted by the Association of School and College Leaders (ASCL) and the Times Educational Supplement (TES) reveals a bleak picture of the unhappiness within the teaching profession.
ASCL general secretary Brian Lightman said the union's members are facing a "barrage of criticism" and feel they are "on the verge of being bullied".
Two thirds of the school leaders polled (66.4%) said they are not as happy in their job now as they were 12 months ago.
Some 60.8% said that the Government's education reforms will have a detrimental impact on standards of education, whilst just 4.8% said the policies would improve standards.
Around a third (34.4%) said it would have little impact.
The survey also found that almost half (45.8%) believe that changes to Ofsted inspections will have a detrimental impact on standards.
Under the changes, all schools will face unannounced visits, outstanding schools that do not have the top grade for teaching will be reviewed and the satisfactory rating will be scrapped and replaced with "requires improvement".
More than two thirds (67.9%) of those questioned agreed that the government's attitude to the teaching profession has made them more likely to quit in the next five years.
The poll, published as ASCL members prepare to meet in Birmingham on Friday for their annual conference, reveals that over a third (36.7%) are actively planning to leave teaching, while more than half (54.4%) are considering it.
Almost half (49.7%) of the heads surveyed said they would not recommend taking on a headteacher's post to their colleagues.
The survey suggests that many secondary school leaders are worried about the government's education policies.
Asked which is their biggest source of concern, 37.7% cited changes to Ofsted inspections while 32.3% said changes to the government's education policy.
Some 16% said their biggest worry was the financial pressure on schools while 14% highlighted their increased workload.
Just 7.1% said that the government recognises the work that school leaders do, with 88.8% saying they do not think this is the case.
And 91.5% do not think that the government is supportive of the teaching profession.
Lightman said: "Our members feel they're facing an endless barrage of criticism, calling into question their commitment.
"They feel angry and deeply frustrated, on the verge of being bullied. They are professionals who are absolutely committed but they can only take so much. They want to work with the government to continue to improve standards but instead they are being treated as part of the problem.
"The government has cherry-picked international statistics, made sweeping generalisations and painted a caricature of schools as failing in order to justify its policy decisions. This must stop."
"Untold damage will be done to our young people's future education if the toxic rhetoric is allowed to continue."
A Department for Education spokesman said: "Thousands of heads are doing a good job, often in challenging circumstances. We're undertaking a major reform programme and their skills and experience are vital. That's why we are making their lives easier - by giving them more day-to-day freedom; slashing bureaucratic paperwork; and by giving them more control over discipline.
"We cannot ignore concerns about standards. Employers and universities quite rightly want our curriculum and exams to measure up to the best in the world. We have slipped down the international performance tables and we must rectify this.
"Too many children are leaving school without the numeracy and literacy skills they need in life. We want to work with head teachers to raise standards so that the education our children receive is world class."