Teaching unions were on a collision course with Schools Secretary Ed Balls over Sats tests today after announcing they are to ballot members on a boycott.
The National Union of Teachers (NUT) and the National Association of Head Teachers (NAHT) said they were "saddened" that the Government had failed to respond to their calls for the tests to be abolished.
National curriculum tests - known as Sats - in English and maths are taken by 11-year-olds in their final year of primary school.
The unions 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.
Any action would be highly embarrassing for the Government as it is likely to fall around the time of the general election.
Both unions say they have put forward "clear and positive alternatives" to the current testing system.
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."
The unions said the aim of any industrial action would be to "frustrate" the administration of the tests, which are due to take place during the week beginning May 10. There will be no strike action, they said.
Children will go to school as usual but, instead of taking the tests, will have a normal teaching 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.
NAHT general secretary Mick Brookes said: "We have put forward a viable and professional alternative which would have improved the assessment process and ensured that no child leaves the primary phase with incorrect grades.
"The current system has resulted in thousands of children moving to the next phase of their education 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."
Ministers said any move towards a boycott is "irresponsible" and insisted that any industrial action would be unlawful.
In the NUT's indicative ballot, which saw a turnout of just under 25%, 76% of responding members said they would support a boycott.
And the NAHT's first survey of 22,000 members showed "strong support" for a boycott.
The two unions originally passed resolutions at their annual conference last year, proposing the action if the tests are not scrapped
They want to see Sats replaced by teacher assessment and argue that the tests are bad for children, teachers and education, and cause unnecessary stress.
They also want to see school league tables abolished.
In November, Mr Balls left the door open for Sats to be scrapped when he announced that teacher assessment of pupils' achievement will be published alongside Sats data in achievement and attainment tables in future.
Schools Minister Vernon Coaker said: "I am very disappointed that NAHT and NUT think a boycott is in children's best interests.
"Following my recent meeting with Mick Brookes I wrote to him welcoming the considerable progress that together we have made in strengthening the role of teacher assessment and ensuring more information is available to parents.
"I made clear that we are committed to improving the assessment and accountability system to ensure it is fair to schools and teachers; provides the best possible picture of the progress made by every pupil; provides parents with more information about the performance of their child and of local schools, and hold schools accountable in a way that better reflects their context and the breadth of outcomes that they achieve for their pupils."
He went on: "I believe these are the shared objectives of parents, head teachers and teachers around the country.
"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."