Schools are to face widespread disruption after teachers voted to stage further strikes, starting with a national walkout in the summer, in a bitter row over pay, pensions and conditions.
The National Union of Teachers (NUT) vowed to step up their campaign of industrial action at their annual conference in Brighton.
The move leaves hundreds of thousands of schoolchildren across England and Wales facing the prospect of school closures and disruption to lessons.
Delegates backed a priority motion which calls on the union to co-ordinate national strike action in the week beginning Monday, June 23, if "significant" progress is not made in resolving the long-running dispute.
The NUT has said it would not rule out more than one day of strikes, and the resolution also left the door open for further action in the autumn.
The Department for Education has previously condemned the union's strike action, saying it disrupts families and holds back children's education.
The resolution was backed by a large majority but was not passed unanimously.
Afterwards, delegates stood up cheering, and, in a reference to UK Government education secretary Michael Gove, chanted "Gove must go".