Teachers have voted overwhelmingly for a one-day national strike in June.
The NUT union members, meeting for their national conference in Brighton, are fighting Tory education secretary Michael Gove's attacks on their pay, pensions and conditions.
The amended motion passed instructed union leaders to "draw up plans for a national strike in the week beginning June 23rd" if "significant progress" has not been made.
It added that the union should seek to coordinate with other unions and show "flexibility" to their timescales.
The motion also instructed the union to "consult with members about a series of strikes through the autumn term".
It announced a lobby of parliament on 10 June and committed to mobilise for a People's Assembly protest on 21 June.
Delegates stressed the need to fight. Cleo Lewis from Greenwich said, "I'm exhausted. The pressure is ruining my life. My family's lives. The lives of the children that I am teaching."
Delegates took part in a heated debate about whether there should be more hard-hitting action on Saturday.
One amendment called for at least four days of strikes in the autumn term along with a series of demands to improve teachers' pay and conditions.
Delegates who opposed the amendment said it was "unrealistic".
Jess Edwards from Lambeth backed the amendment. She said it was important to "recognise the strengths of the campaign so far".
But she said, "The debate is about the way forward. We have to go beyond protest and win."
Union leaders argued against the amendment and it lost. Yet some 36 percent of conference delegates voted for it on a card vote.
Andrew, an NUT member in Rotherham, South Yorkshire, told Socialist Worker, "In my school a lot of teachers are disaffected with the union leadership.
"On 30 November 2011 the strike was very well supported. But after that a lot of younger teachers drifted away as they thought the union had no strategy.
"I don't understand why they didn't roll it on. We need to up the ante. We need to strike for two days—and tell Gove that if he still doesn't listen, we'll be out for three days."
Some in the union, including on the left, argued that there wasn't enough backing nationally to successfully escalate the action. They said that sustained teachers' strikes were possible—but not now.
Paul McGarr is an NUT rep in Tower Hamlets, east London. He told Socialist Worker, "Union leaders point to unevenness among teachers. But in most areas the strike on 26 March was very good. And putting forward a strategy that can win holds out the prospect of overcoming that unnevenness."
NUT president Max Hyde ruled that amendments calling for two days of strikes in the summer term and to begin a debate on "the possible use of indefinite strike action" would not be heard.
This followed a very close vote on whether to hear the amendments.
Teachers have shown their willingness to fight in every strike ballot and their ability to hold successful action in every walkout.
Anne Lemon from the NUT's NEC stressed that teachers could still escalate their action.
"Michael Gove will be listening to see how our strike action will be escalated," she said. "And it is possible within this motion for that to happen.
"The motion does not exclude us from taking action with other unions. There's nothing that precludes that in this motion.
"If we take strike action one day and one day six months later, and we don't make progress, we have two choices. One is give up. The second is that we step up.
"Our members are for stepping up."