Government plans to test 11-year-olds on their spelling and grammar have drawn fierce criticism from school leaders, who warned the move is a waste of taxpayers' money.
The National Association of Head Teachers (NAHT) raised the prospect of a future boycott as they voted to explore ways of making sure the "flawed" exam does not take place.
It came as NAHT general secretary Russell Hobby said the union could snub the Government's controversial new reading test for six-year-olds if it is used "as a stick to beat schools with".
From next year, pupils in the final year of primary school will sit an externally marked spelling, punctuation and grammar (SPAG) paper as part of their national curriculum (SATS) tests. But the NAHT believes that youngsters' writing abilities are better measured through teacher assessment.
At the NAHT's annual conference in Harrogate, delegates passed a resolution which warned: "The proposed tests in technical English are a case of replacing one set of tests with another and a waste of tax payers' money. Their outcomes can be achieved through moderated teacher assessment in writing. Conference instructs National Executive to explore available means to ensure this flawed test does not take place."
The Government argues that too little attention has been paid to spelling and handwriting in the past decade. In 2010 the NAHT, alongside the National Union of Teachers (NUT) staged a boycott of SATS tests, insisting that they were bad for children, teachers and education.
Shortly after, the new coalition government established a review of the tests, led by Lord Bew. As a result of the review, for the first time this year the SATs writing test has been scrapped, with teachers assessing pupils' work instead, alongside a beefed-up spelling and grammar test.
The writing paper had come in for heavy criticism, with concerns that it was hard to mark and that pupils were being drilled to pass it, preventing them from expressing their creativity. The move was welcomed, but headteachers now fear the new externally marked SPAG test will simply replace teacher-assessed writing.
Mr Hobby said: "The worry is that you're giving with one had and taking away with the other, and it will end up as simply another test. Heads are keen for the writing test to remain as teacher assessed."
A Department for Education spokeswoman said: "Too little attention has been given to spelling, punctuation and grammar over the last decade. That's why we have accepted Lord Bew's recommendation to assess spelling, punctuation, grammar and vocabulary as part of the writing test at Key Stage 2."