Education ministers are "alienating the profession, disempowering teachers" and are responsible for gaping holes in staff numbers, a union leader has warned.
Dr Mary Bousted, general secretary of the Association of Teachers and Lecturers (ATL), said the Government's education reforms – including plans to strip schools from state control under its controversial academy proposals - are "breaking the public service ethos" of the profession.
In her keynote speech at the ATL's conference in Liverpool, during which she described the national curriculum as "insane", Dr Bousted identified increasing workload and falling staff numbers as typical of the problems in education.
She received the first of several rounds of applause from delegates when she said: "I can think of no time where teachers, lecturers and school leaders have felt less involved, less consulted and less able to exercise their professional judgment than now.
"Do you know - education ministers should give themselves a medal. They have succeeded in alienating the profession, disempowering teachers and driving them away from teaching.
"It's some achievement when 50,000 teachers, 11% of the profession, left teaching last year - driven out in droves by Government incompetence and mismanagement."
Research carried out by the union showed four in five teachers have thought about leaving the profession as concerns about workload escalate.
Some 83% of 900 respondents said they had considered leaving teaching. Among them, almost nine in 10 (87%) said this was due to workload.
Dr Bousted said: "Primary school teachers are not known for their rebellious nature. So why are so many now telling me that their job has become impossible, that they no longer enjoy their work and that they want to leave the profession?"
She described baseline tests for four- and five-year-olds entering the education system as "nonsense", while she said Key Stage 2 writing assessments were "a farce" due to the number of clarifications issued to teachers on the subject by the Government.
She added: "And it is not just a problem of assessment. The curriculum is insane.
"It is designed by people who know nothing of how to promote enjoyment of, and development in, writing abilities."
Dr Bousted said she had received concerned letters from parents about pupils' mental health. It came as a report produced for the ATL conference showed primary school pupils are being driven to self-harm due to anxiety caused by pressures at school and on social media.
The ATL general secretary said: "I am afraid, they are right to be worried. Because the incidence of childhood and adolescent mental ill-health is rising.
"I am not surprised that our children and young people are becoming ill. They are increasingly negatively affected by an education system which is dominated by the test mania which the Government is promoting."
Dr Bousted said forced academisation – the cornerstone of the Government's education white paper - was more to do with "breaking the public service ethos of the profession" than raising educational standards.
During a 42-minute speech, she said schools watchdog Ofsted is "no longer fit for purpose" because it did not give "accurate, valid judgments of a school's effectiveness".
She added: "We must fight together to protect our profession, for the sake of the children and young people whose education depends on us.
"And we will fight and if we fight together, with parents and councillors, with other unions, with politicians, with governors, with the whole of civil society which opposes the madness of forced academisation, then this is a battle we can win."
The ATL conference, which runs until Wednesday, saw delegates heckle and jeer schools minister Nick Gibb during his appearance on Monday.
In a statement, a Department for Education spokesman said: "While we're pleased Dr Bousted has acknowledged the work we're doing to reduce unnecessary work for teachers, it's a shame she focuses on negatives and doesn't show more pride in the work of her members and all the other teachers whose hard work and dedication has driven such improvement in recent years - with 1.4 million more children in good or outstanding schools than in 2010.
"We are creating a dynamic school-led system in which under-performance can be addressed swiftly and decisively, and where parents can play a more active role in their child's education. Under this system, improvement is driven from within and through strong schools spreading their influence to support struggling areas, and driving up standards by working together in multi-academy trusts (MATs) to share resources, staff and expertise.
"The vast majority of schools which have become academies are now thriving. In the minority of academies that under-perform, we can take swift action to secure improvements."
Support for academisation has been hard to find from teaching staff, who staged marches around the country in defiance over the plans.
Labour said the scheme would face a £1.1 billion funding shortfall, an accusation described by the Government as "completely untrue".