Teachers have refused to rule out the prospect of going on strike over serious concerns about "intolerable" classroom workload.
Members of the National Union of Teachers (NUT), meeting at the annual conference in Brighton, agreed to consider industrial action over pressures driven by increasing student numbers, a growing teacher shortage, and reduced funding for schools.
They said greater support is needed from Government for beleaguered schools and teaching staff.
In an impassioned speech, Laura Fisher, a teacher from Wakefield, said the situation was so bad that pupils have asked her if she sleeps in work due to the amount of time she spends in the classroom.
She said: "I know striking is a difficult subject, it is still the biggest debate within ourselves.
"People say, 'I didn't become a teacher to strike'.
"But every day I strike, I am teaching children the biggest lesson of all - that their education is worth fighting for."
Members voted in favour of a motion "building a campaign to persuade members that national strike action will be necessary to bring about changes in the intolerable working conditions, and lack of work-life balance, created by current Government policies".
It contained the pledge that the union "should continue to give full support, up to and including sustained strike action, to school groups which seek to win local improvements on workload".
Strike action can only begin after a ballot of members.
An amendment proposing to begin preparations for an immediate ballot if negations with the Government are not fruitful was not heard.