A headteacher is quitting the profession after 23 years over claims schools are now "factory farming" children and failing to prepare them properly for a successful future.
In an impassioned resignation letter, Kit Messenger, of Manor Field Primary School in Burgess Hill, West Sussex, criticised the "progressively fragmented educational system".
And, in a withering attack on education policy, she laid into moves to narrow the curriculum, which she said had led to schools being judged on only reading, writing and mathematics.
Ms Messenger, 45, said the Government's push for schools to become academies reinforced her belief to quit 530-pupil Manor Field - a decision she described as "heart-breaking".
She also admitted finding it difficult to protect her staff from heavy workloads that left them little time outside the classroom for their families.
And, in a brutally honest assessment of the education system, she said the toll of completing "bureaucratic tasks" had affected her own physical and emotional health.
In the letter, she said: "Unfortunately, despite all of your support, in the current educational climate I no longer feel it will be possible to achieve my vision for children at Manor Field School.
"The narrowing of the curriculum, to the detriment of all other subject areas, has increased signiﬁcantly over the past two years.
"Judgments made of schools are now so restricted to a small set of measures that the pressure to focus only on reading, writing and mathematics has become untenable and I have increasingly felt that we are 'factory farming' our children and failing to prepare them adequately for a successful future in this changing world.
"The recent announcement that all schools should become academies has further strengthened my belief that now is the time to leave a career that has been central to my life for 23 years.
"I strongly believe in a state system in which all children have access to a good, rounded education and where staff are treated with respect and enjoy fair working conditions. I do not believe this will be possible under our progressively fragmented educational system.
"I have been passionate about my career for more than 20 years, putting it ahead of everything else in my life. My love for teaching and school improvement has run like blood through my veins and I have constantly sacriﬁced friendships and family life in order to secure better provision for children.
"I now ﬁnd that much of my work is spent completing bureaucratic tasks which have no or little positive impact on our pupils and this has left me feeling increasingly frustrated and unhappy. It has now begun to have a detrimental impact on my physical and emotional health.
"I have also found it progressively difﬁcult to protect staff from workloads that leave little time for their own families, feeling that the only way to secure good outcomes at inspection is to push them further than I believe is reasonable.
"The decision to resign from the post of headteacher and bring to an end a career that I have loved so very deeply has been incredibly difﬁcult. It is no exaggeration to say it has been heart-breaking. However, I do know it is the right decision."
The school's board of governors said they "fully understand and support" her reasons for stepping down, which will happen in August.
They said in a statement: "Ms Messenger clearly explained that recent plans by the government for education are contrary to her own beliefs that all children should have access to a wholly rounded education.
"Ms Messenger has spent the last 16 years of her teaching career at Manor Field School and has worked tirelessly to create a caring and effective learning environment."
West Sussex County Council said it was "saddened" to learn of Ms Messenger's resignation, adding it regretted losing any experienced and respected headteacher.
Thanking her for her years of hard work, the council added: "The decision to resign is a personal matter and, whilst it is not appropriate for us to comment on her resignation, we respect her right to express her reasons.
"We are writing to the minister to express our concerns regarding the recent government white paper. In particular we feel there is not a strong enough voice for the parent and child in the approach.
"We believe families are entitled to a choice - whether that be academies, free schools or local authority schools - and that one-size does not fit all. Above all we think educational matters should be decided on locally and not nationally."
A Department for Education spokesman said: "It is disappointing to hear of any headteacher choosing to leave the profession. Our reforms are raising standards and thanks to the hard work of teachers there are a record number of children in good or outstanding schools - 1.4 million more since 2010.
"We want that trend to continue which is why the proposals in our White Paper will put power back in the hands of the teachers and school leaders who know their pupils best, alongside new measures to more swiftly tackle failing and coasting schools. Our reforms have given teachers the freedom to innovate and develop exciting lessons that inspire pupils.
"We know mastering the basics of literacy and numeracy at primary school has a huge impact on how well children do at GCSE, which is why we are determined to raise standards. We have updated the Key Stage 2 tests to reflect our new, more rigorous curriculum which will help every child fulfil their potential regardless of their circumstances. Tests help teachers identify and provide the support pupils need as well as giving parents a picture of how their child is doing."