The NUT could stage a boycott of new baseline tests for four-year-olds in order to defend a play-based early years curriculum.

An amendment to a motion being debated at the union’s annual conference tomorrow will call on the NUT executive to “investigate the possibility of a mass campaign of principled non-compliance with any policies which erode children’s right to play in the early years”.

The main focus of the union’s ire is the introduction of a new test for children in their first term of primary school, against which their academic progress can be assessed. It is due to be introduced in 2016.

An amendment to a motion on the issue, which will go before the conference in Brighton, warns that the tests “can only cause stress and anxiety to children at the most formative stage of their school life”.

The main motion also warns of the “damage that a school starting age of four can do”, and instead calls for a play-based “developmentally appropriate foundation stage for children between the ages of three and seven”, before the start of more formal schooling.

This comes in stark contrast to recent calls from Ofsted for schools to provide early years education for children as young as two, to prevent youngsters from deprived backgrounds falling behind their peers.

Ahead of the debate, NUT executive member Hazel Danson, a primary school teacher in Huddersfield, said the union’s leadership was minded to support a boycott of the tests.

“We would look seriously at... a trade dispute. [For] any sort of non-compliance action we would ballot [members], but I would have every confidence that a ballot on this issue would be very strongly supported.”

Ms Danson added that younger children benefit from play-based learning, which develops their social and motor skills to prepare them for school.

“We’re starting them ever younger and forcing them into this quasi-school formal setting, when developmentally it’s actually quite damaging to good child development,” she said.

“The way you get them to be school ready is not to give them a quasi-formal schooling too young, because they need developmental competencies that make them ready for learning.”