A "pressure cooker environment" in schools is affecting children's mental health and self-esteem, a charity has said.
Young Minds voiced concern following a report commissioned by the National Union of Teachers which found exam stress is leading some pupils to self-harm as children are tested at younger and younger ages.
Some 8,000 teachers were surveyed into the impact of exams, and the findings showed that unprecedented levels of school-related anxiety are affecting children in primary and secondary schools.
Lucie Russell from Young Minds said the findings were "very concerning as they demonstrate that both pupils and teachers are under a lot of pressure to achieve results in a pressure cooker, exam factory environment".
"Constant testing and assessments are creating an environment which is putting a lot of stress on young people and adversely affecting their confidence, self-esteem and mental health.
"What we need to do is create an education system whose success is not just assessed by exam results, but by how it is helping to develop children's and young people's character, resilience and wellbeing."
She added: "Young people tell us they feel completely defined by their grades and that they're a failure if they don't get what everybody thinks they should be getting."
Emeritus Professor Merryn Hutchings, who conducted the research, said that the Government's emphasis on academic subjects such as Maths and English was narrowing the curriculum, and meant pupils were sitting exams regardless of aptitude or interest.
She also found that pupils were under pressure to learn things before they were ready, giving children a sense of failure at even younger ages.
Prof Hutchings said some schools had attainment results and progress charts displayed on the walls for all to see, and that children were being tested at increasingly young ages.
"Four and five-year-olds are being tested on phonics... at an age when most European countries haven't even started formal schooling."
The report also found that nine in 10 teachers think that pupils become stressed and anxious in the time leading up to SATs exams - taken in year two and year nine - while 80% of teachers said that the emotional and social aspects of education were neglected because of the need to focus on academic targets.
One teacher in an "outstanding" Ofsted-rated primary school commented in the report: "It is heart-breaking to have a four-year-old approach me in tears because they 'are still in the bad group for reading' because they have already been streamed in phonics at age four!"
Another teacher said a "severely dyslexic" and "incredibly hard working" year six pupil turned to physical self-harming because of the "pressure she felt to achieve to a level similar to that of her peers", and another commented that self-harming is "rife" in pupils aged 14-16.
Pupils interviewed for the report spoke of exam stress and their worries about performing well. A year 12 student said some people would cry for most of the exam because they were so stressed.
A Department for Education spokesperson said: "Part of our commitment to social justice is the determination to ensure every child is given an education that allows them realise their potential.
"That's why we are raising standards with a rigorous new curriculum, world class exams and new accountability system that rewards those schools which help every child to achieve their best."