By Hannah Goff
BBC News at the NUT conference, Manchester
Teachers say testing makes some children give up trying
Tests and league tables have made England's children the unhappiest in the western world, teachers have said.
Even nursery-age children were being taught to spell and write in readiness for the tests waiting for them at primary school.
Very young children knew exactly what educational levels they had reached, and many stopped trying because they believed they were "dumb", they said.
The government has denied that children have to take too many tests.
Delegates at the National Union of Teachers conference in Manchester heard that children were being streamed from the first year of primary school.
It also heard that they faced increasing pressure from intensive monitoring.
Sara Tomlinson, a teacher from a school in Lambeth, south London, said: "They all know their own level - they walk around schools almost with their level printed on their foreheads."
She also argued that schools were only focusing on those pupils who were likely to meet the targets because they were the only ones who counted for their league tables positions.
Another delegate Netta Ford said: "Sats were the poison at the heart of the education system – they turn teachers into robots and they turn children off learning."
Children are tested at the ages of seven, 11 and 14, but many teachers say they spend much of their school life preparing for them.