Teachers are set to raise the prospect of a boycott of primary school tests warning that a "testing culture" is damaging children.
Testing and labelling of children as "successful" or "failing" makes it harder to motivate and educate pupils, according to a resolution due to be debated by the National Union of Teachers (NUT) at its Easter conference.
Union members are expected to raise concerns at the Brighton meeting about assessments taken by primary-age youngsters, including the new "baseline" tests for four and five-year-olds, a reading check taken at the end of Year 1, and SAT tests.
The Government has argued that testing is important to help ensure that youngsters leave primary school with a good grasp of English and maths.
The NUT's motion, one of several listed on primary education and the impact of testing, says: "The testing culture in primary schools causes undue stress on teachers and is extremely damaging to the emotional health and wellbeing of children.
"Many parents, teachers, academics and other professionals have noted an increase in stress-related conditions in very young children and high levels of anxiety and stress particularly in the time leading up to formal tests."
The resolution - one of several listed on the issue of primary testing - calls on the NUT's executive to take a number of steps, including balloting members in primary schools for a boycott of baseline tests this year.
The literacy and numeracy checks, which are not mandatory, take place weeks after infants start in reception. The assessments were piloted last autumn and ahead of formal introduction this year. The results will be used to chart children's progress throughout primary school.
The motion also calls for the executive to "consider a ballot for the boycott of all statutory tests within primary schools in 2016".
A second resolution argues that testing has a "detrimental effect" on pupils, especially those in primary schools, forces schools to teach to the test, narrows the curriculum and "limits the educational experience for pupils".
It calls for a campaign against all testing, and urges the union to ballot members between the end of June and August next year for a boycott of all primary assessments in 2017/18.
NUT general secretary Christine Blower said: "We are really concerned about the whole exam factory attitude to education. It's happening in primary schools now as well as secondary.
"It's massively demotivating to teachers that they have to focus so much on testing outcomes to the detriment of the rest of the curriculum."
A Department for Education spokeswoman said: "Parents rightly expect us to ensure that their children are leaving primary school having mastered literacy and numeracy and that is why we have tests at the end of Key Stage 2.
"The recent OECD skills survey showed that too many of our young adults failed to master these skills when they were in school. We're determined not to let that happen to another generation of young people - we want to see all children pushed to reach their potential. In order to do that, and to recognise the achievements of schools in the most challenging areas, we want to measure the progress that all pupils make as well as their overall attainment.
"We are always willing to listen to the views of teaching unions and are in regular discussion with them, working with them to ensure that this transition year goes smoothly.
"It is disappointing to see that the NUT are taking this approach, which would disrupt children's education, rather than working with us constructively as other unions have."