Kenny Frederick, head of 1,250-pupil George Green's School in east London, was speaking at a seminar organised by the Joseph Rowntree Trust in association with The TES.
"Primary schools in our area make every effort to get pupils through the tests at 11, but it isn't sustainable," she said. "When they arrive at secondary school, they don't have the general knowledge, social skills or the ability to work in teams that they need to cope with the curriculum. The key stage 2 tests are a real barrier."
More than 60 per cent of George Green's pupils are on free school meals. "We feed 200 for breakfast. We have to wash some of them. And we have to deal with their anger before we can get them into the classroom," she said.
The starting point of the seminar was the trust's research into the relationship between education and poverty. A paper published in September found that poverty was a strong predictor of educational achievement and that school accounted for only 14 per cent of the difference in pupils' performance.
It also showed that pupils who grow up in poverty tend to be less confident about school and to take part in fewer after-school activities.
William Atkinson, head of Phoenix school in west London, told the seminar that outstanding teachers were the key to raising achievement. "They should not just be technically great. They also have to care," he said, and they should be paid much more.
A report on the issues raised at the seminar will be presented at the Department for Children, Schools and Families on November 29.
Kenny Frederick, page 29.