A proposed national boycott of Sats tests could be called off if the Government delivers on its pledge to reform school league tables, the NUT has said.
The union will reconsider its support for the proposed boycott if league tables cease to be seen as the "be all and end all", said Christine Blower, its acting general secretary.
Her comments, which appear to soften the union's stance, come as its annual conference starts in Cardiff today. Members will be given a vote on taking industrial action to boycott primary school tests in 2010.
The remarks also come in the same week that Ed Balls, the Schools Secretary, made his strongest statement yet about the need to change the current Sats regime and improve school accountability.
Ms Blower said she was confident the boycott proposal would win the backing of members.
"What is as yet unproven is if we will need to do the boycott in light of fresh comments from the Government that the tests are not set in stone," she said. "We are not interested in a boycott for the sake of it. We want a change to the way children are assessed and we want to get rid of league tables.
"If we hear something helpful, we will reconsider our position. We would need to hear that assessment was going to be done in a different way and that league tables would not be the be all and end all."
Ms Blower's tone is in contrast to statements from the NUT and the National Association of Head Teachers when they announced the boycott proposal last month. They called for a review of testing and accountability that would replace testing with teacher assessment.
They also demanded the introduction of a national sampling scheme to check standards in English, maths and science, and said the introduction of "when ready" tests would not halt the boycott.
The move was criticised by other teachers' organisations, which said that aggressively confronting the Government could make ministers less likely to introduce changes.
But Mr Balls made his clearest commitment yet this week to changing Sats for 7- and 11-year-olds.
He said he would wait for the findings of an "expert group" set up to advise on testing before deciding what action he would take, but added: "I would be very surprised if they said there was nothing at all you could possibly do to make the current key stage 2 tests better.
"The Government has no intention of getting rid of assessment altogether. The most important thing is the way in which the tests are used and the accountability regime. The accountability system needs to change if you keep KS2 tests or not."
A pilot of "when ready" tests is being carried out in 100 schools. But Mr Balls ruled out the possibility that they would be ready to be introduced next year.
The Department for Children, Schools and Families published a survey claiming strong parental support for national tests, with 70 per cent of respondents saying they provided valuable information.
But less than half of parents thought the tests should stay as they are; nearly a quarter said the tests did not reflect their child's progress.
A separate survey of primary staff, published at this week's annual conference of the Association of Teachers and Lecturers, reported widespread concerns that there is too much testing in primaries and not enough time for play.
Three-quarters of teachers said KS2 tests had a negative impact on pupils' confidence, and almost eight out of 10 said it damaged their enjoyment of learning.
The poll of 740 teachers found that 30 per cent thought compulsory education should not start until children are at least six years old.
Delegates at the conference complained about the high proportion of secondaries still administering KS3 tests for 14-year-olds, even though they were abolished last October. It is estimated that three-quarters of schools are continuing with the tests.