Headteachers passed a vote of no confidence in the Government's education policies on Saturday.
Many of education secretary Michael Gove's reforms are "not in the best interests of children", according to delegates at the National Association of Head Teachers (NAHT) conference in Birmingham.
The union raised particular concerns about the new national curriculum, major test and exam reform and schools being forced into becoming academies.
Tim Gallagher, proposing the motion, said: "Enough is enough. This motion's intention is to send the strongest message possible to this government that many of their education policies are failing our children, their parents and the very fabric of our school communities."
Earlier, the NAHT's president, Bernadette Hunter, likened the education secretary to a "fanatical personal trainer" urging headteachers to go "faster, faster, higher and higher".
The NAHT is the first headteachers' union to pass a vote of no confidence in the Government's education reforms.
The UK's three biggest teachers' unions, the Association of Teachers and Lecturers (ATL), the National Union of Teachers (NUT) and the NASUWT passed similar votes at their Easter conferences.
The NUT and the NASUWT are already planning regional strikes in the North West next month in a continuing row over pay, pensions and workload with the prospect of a national walkout looming in the autumn.
The latest vote of no confidence is a further sign of the worsening relations between the Government and the teaching profession.
Gove is expected to defend his education reforms when he takes part in a question and answer session with headteachers at the conference later this afternoon.
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