Teachers are on the verge of voting to boycott key primary school tests amid concerns over the pressure it puts on pupils.
Delegates at the National Union of Teachers (NUT) annual conference in Cardiff will on Monday look to pass a resolution to "support and promote a parent boycott" of the 2017 national curriculum tests for primary school children, known as Sats.
They will also vote to ballot members over a protest against all primary school tests for the 2017/18 school year.
The motion was listed for consideration on Sunday, but conference delegates - all of whom spoke in favour of action - ran out of time.
It forced the rest of the debate - and the crucial vote - to be postponed by a day, although delegates did have time to vote in favour of an internal ballot of NUT primary members over a boycott.
Speaking for the resolution, teacher Benjamin Guy, from Nottinghamshire, said: "We have been here before, time and time again.
"We must show the Government and parents that we are willing to take actual, tangible action to oppose destructive, fundamentally broken testing.
"The time for consideration is over.
"We have to stand tall and actually produce something to protect the mental health of our students from the excessive pressure of these demoralising and destructive Sats tests."
It comes just weeks after the Government announced plans to scrap national curriculum tests for seven-year-olds.
Any vote in favour of the boycott would mirror that of the Association of Teachers and Lecturers, where members at its annual conference in Liverpool this month voted for similar action.
The unions are to merge later this year.
Kevin Courtney, NUT general secretary, said: "What I heard this morning was teachers giving you their professional assessment of what the assessment system is doing in schools. They want a change.
"Many of them also said teachers aren't against testing - they were speaking in favour of a positive alternative.
"They were saying a boycott would be a completely defensible, moral position to take to stop this happening to our children - and they're right to think that."
Last year 47% of primary school pupils in England failed to meet the new required standard in reading, writing and maths, Sats data showed.
It would not be the first time pupils have been involved in a protest against Sats.
Back in 2010 the National Association of Head Teachers (NAHT) joined the NUT in a boycott of primary school testing, after ballots of their leadership members showed support.
It was down to individual heads, deputies and assistant heads to decide whether to take part.
Around a quarter of primaries in England were involved in the action, with tens of thousands of youngsters missing the tests.
Last spring, there was a parent-led campaign to keep children off school during Sats week, with organisers arguing that there is more focus on testing, results and league tables than children's happiness.