Pupils' learning is narrowed by tests, say the unions
Teachers' unions in England are to ballot members on a boycott of this year's Sats tests for 11 year olds.
The National Union of Teachers and the National Association of Head Teachers have called on the government to scrap the tests, saying they narrow learning.
Head teachers' union leader, Mick Brookes, said the primary school tests unfairly labelled schools as "failing".
Schools Minister Vernon Coaker described the threat of a boycott as "disappointing".
Mr Coaker said it was "nonsense" to say the tests were meaningless and attacked the "myth that children spend their entire primary school career preparing for the tests ".
This ballot to stop the Sats could set these teachers' union on a collision course with the government in the run up to the general election.
However the other large classroom teachers' union - the NASUWT - says it wants to keep the tests.
But the NUT and NAHT are now pressing ahead with plans for a full ballot of members after indicative ballots at the end of last year showed widespread support for a boycott.
In a joint statement, the NUT and NAHT said the action, short of a strike, would be intended to "frustrate the administration of Sats".
NUT general secretary Christine Blower said: "The lack of a positive response from government is disappointing. We want to avoid industrial action and call upon the government, even at this late stage, to enter into meaningful talks."
Mick Brookes, NAHT general secretary, said: "The current system has resulted in thousands of children moving to the next phase with misleading information about their ability.
"It has also led quite unjustifiably, to schools and their communities being labelled as 'failing' with the consequence of damaging recruitment of head teachers and worsening their working environment."
If a boycott goes ahead, children would attend school during Sats week in early May, but instead of taking tests they would have a normal school week.
Both unions said they give parents an "absolute guarantee" that their child's progress will still be accurately reported by schools taking part in a boycott, and the information passed on to secondary schools.
The Sats tests are taken each year by about 600,000 pupils in England and the results are used for the annual primary school league tables.
In previous years, pupils have taken tests in English, maths and science - but the test for science has been removed.
The Schools Minister rejected the criticisms of the tests.
"It is nonsense to claim the tests are meaningless. Our Expert Group reported last year that it would be wrong to scrap tests and that they are educationally beneficial and give parents objective information on their children's progress.
"It's time to challenge the myth that children spend their entire primary school career preparing for the tests - the fact is that from this year, children will do just two externally marked tests before they are 14.
"We've made it repeatedly clear that drilling with practice test papers is wrong. The best schools show that excellent teaching throughout the year is the best preparation for test - that's why we have been working with teacher organisations on clear guidance to make sure that it doesn't happen."