By Angela Harrison
BBC News education reporter at the NAHT conference
The Sats results are used to make league tables
Head teachers have voted in favour of balloting their members on whether they should boycott next year's Sats tests in England.
It came shortly after Schools Secretary Ed Balls called on them not to take what he called irresponsible action and vowed to reform the assessment system.
But the National Association of Head Teachers voted in favour of balloting, if all other avenues were exhausted.
The heads argue the tests put pressure on children and narrow the curriculum.
Sats are taken by 11-year-olds in England.
Earlier Mr Balls told the conference of head teachers: "I don't want children and teachers overly stressed about Sats in Year 6."
But he added: "We must ensure that parents and the public get the information they want and need about the progress of every primary age child and the performance of every primary school."
He urged heads to work with him to improve the testing regime but insisted "it would not be right to abolish Key Stage 2 tests." This drew a cry of "rubbish" from one of the delegates.
And he told them a boycott of the tests would set a bad example to children.
Mr Balls had been quite well received and was applauded by the heads, but he could not persuade them to abandon their plans and 94% voted for a ballot.
Earlier, the president of the National Association of Head Teachers, Chris Howard, said there would be no end to its campaign until the "tyranny of testing and league tables" was over.
Head teachers and classroom teachers all dislike the tests and most of all the league tables made from them.
They say teachers are forced to "teach to the test," focussing most on the three subjects tested, English, maths and science.
Children and schools are both put under too much pressure over the tests, they say.
In other parts of the UK, children are tested but the tests are marked in school and are not used to make league tables.
At the Naht's annual conference, its new president, Mr Howard, told delegates: "There will be no conclusion to our honest and well-reasoned campaign to stop the tyranny of testing and tables for primary schools in England until they have been ended."
And he suggested it was "high noon" for the government, which he said had promised "education, education, education", but had delivered "regulation, regulation, regulation."
The organisation says the tests should be replaced by assessment of pupils by teachers, which already takes place.
The National Union of Teachers recently voted to ballot its members on a boycott and this will probably take place in the autumn.
The two groups together make up most of the teaching staff in England's primary schools so a joint boycott by them could throw next year's Sats into disarray.
Their action comes after the embarrassing shambles of this year's tests, when marking problems led to severe delays in publication of hundreds of thousands of children's test results.
The government went on to scrap compulsory tests for 14-year-olds.
'Set to quit'
Gail Larkin, a head teacher from Epsom in Surrey, was delighted with the conference vote.
She had challenged Mr Balls, saying the publication of the league tables led to "public humiliation of schools".
Afterwards, she told BBC News she was prepared to resign in the summer if Sats were not abolished.
"I can no longer stand by and see pupils in Year 6 be pushed through a curriculum which is only focussed on English, maths and science," she said.