Many schools in England will fail to meet the government's targets for improving children's literacy and numeracy, according to a survey of headteachers and local education authorities.

The National Association of Head Teachers (NAHT), meeting for its annual conference in Cardiff this week, has published research which suggests that almost 50% of the local authorities in England are expecting to fail to reach the targets for improving 11-year-olds' reading, writing and arithmetic.

The Education Secretary, David Blunkett, has said he will resign if the government's targets are not reached.

By 2002, 75% of 11-year-olds should have reached Level 4 - the standard expected of their age - in mathematics, and 80% in English. In last year's tests, the equivalent figures were 59% and 65%.

The survey, carried out by researchers at the University of Durham, found that 54% of authorities expect to meet the targets for maths and 51% expect to meet targets for English.

David Hart: "Don't blame our members"

Researchers also found concern among headteachers about how the targets had been imposed. Peter Timms, who led the research, said that some headteachers saw the targets as political rather than educational goals.

"The targets were a blunder and there is little chance schools will achieve them," said Dr Timms.

The union's general secretary, David Hart, said that the bad news for the government in the survey "should not come as a complete surprise. Local education authorities were always going to find their targets for 2002 extremely tough".

Mr Hart will have an opportunity to raise the matter personally with Tony Blair. The prime minister is due to address the assembly this week - the first serving prime minister to speak at a teaching union conference.

The NAHT will be telling the prime minister that he should not regard those who fail to reach their targets as having done a bad job educationally.

Eight in ten 11-year-olds are expected to reach the literacy targets by 2002

According to the union, the burden of the drive to raise standards is falling on schools with average or below average results. It says that targets for small schools, based on percentages, "make no sense".

"NAHT supports target setting as a good management tool, but the inherent dangers surrounding the current national top-down target setting agenda are there for all to see," said Mr Hart.

"The key question is whether the government will respond positively to the results of the survey so that the education experience of all children can be enhanced."

A spokesman for the Department for Education said the government remained confident that the targets would be met.

"The targets are challenging - they are meant to be - but the government has put the resources behind them," he said.

"The targets have the overwhelming support of parents, teachers and headteachers."