Teachers who want to boycott next year's Sats do not have the widespread backing of parents, a poll released exclusively to The TES reveals.
Less than half of parents agree it is appropriate for teachers and heads to boycott the tests, according to a survey carried out by the National Confederation of Parent Teacher Associations (NCPTA).
Just 41 per cent of the parents questioned - more than 2,200 in total - gave their support. More than a third said they disagreed with the proposed boycott, while more than 20 per cent said they were undecided.
The poll is the first in which parents have been asked directly for their views on the boycott. The results show the two unions, the NUT and the National Association of Head Teachers, which have joined forces to call for the action, still have a sizeable job to do to win parents over.
The lack of parental support could raise concerns among teachers considering whether to support the boycott.
The unions have said they will ballot for action unless the assessment regime is overhauled. They have called for national tests to be scrapped and replaced by teacher assessment, arguing that the existing system forces schools to teach to the test and focus on a narrow curriculum.
But David Butler, chief executive of the NCPTA, said the unions had so far failed to make a clear case with parents.
"There is a great deal of angst from the unions about Sats, but if they want to win support from parents, they need to make their objections clearer," he said.
"Parents support the use of tests as a measure of school accountability, so those calling for a boycott need to explain the particular problems with Sats. The unions are entering dangerous territory if they push ahead believing they already have the support of parents. The results show they do not have a mandate."
The poll's findings follow conflicting results of research carried out by the NAHT and the Department for Children, Schools and Families.
The union's survey of more than 10,400 parents found that 85 per cent wanted league tables and national testing scrapped and replaced by teacher assessment.
But the Government accused the survey - distributed by members in their own schools - of being "self-selective" and not representing parents' views.
Officials commissioned their own independent research in which 70 per cent of parents said national tests provided valuable data. But less than half of parents thought the tests should stay as they are, while nearly a quarter said they did not reflect their child's progress.
The publication last week of a government-commissioned review of assessment failed to recommend the changes that the unions are demanding, increasing the likelihood of a boycott.
Christine Blower, the general secretary of the NUT, said parents needed to be reassured that the boycott would not disrupt their children's education.
"We are clear that this is not strike action, but we still need to get that message across to parents," she said. "We are only at the beginning of that process. I am pleased that the support we have is as high as it is."
Big thumbs-up for school report cards
Parents are almost unanimous in supporting the introduction of school report cards, a survey has revealed.
Almost 96 per cent of them said it would be beneficial to have more information than just exam results to judge school performance.
Just over half of parents polled by the NCPTA said there should be one overall score and then a series of individual grades to assess different areas of school performance.
The Government is keen to introduce report cards to offer more information about schools. Details are due to be published next month. They are expected to include measures of attendance, pupil behaviour and satisfaction surveys.
However, three-quarters of parents still want exam results to be published and made publicly available.