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.
Presenting the motion, Ms Fisher told the conference: "If a child knows I'm spending too much time at school, and I know I'm spending too much time at school, how on earth doesn't the Government know?
"I know the books will still be marked. What won't be done is all the little things that make the school unique."
She added: "I want to do my duty, but I don't have time. Nicky Morgan - I'll do my job, but let me get on with it.
"Nicky, my duty is not to you, it's not to my head teacher, it's to the children I serve."
Ken Rustidge, from Lincolnshire, added: "We should be building a national campaign, lobbying, persuading the public and getting the message across in any way possible.
"Crushing workload is a contributing factor in the recruitment and teacher retention problem."
Last month the Government's official spending watchdog found key teacher recruitment targets had been missed.
The National Audit Office found teacher shortages were growing, particularly in poorer areas.
Its report, as an example, found just over one-in-four physics lessons at secondary school level were being taught by staff with only as much as an A-level in the subject.
The Government, in response, said 1.4 million more pupils were being taught in schools rated good and outstanding compared with five years earlier.
Commenting after the debate, Christine Blower, NUT general secretary, said: "Government policies have created the perfect storm for a teacher recruitment and retention crisis.
"Teachers speak of having no life outside of school, nor time for family and friends. We are not talking about having to stay a little bit later of an evening, but of workloads that keep teachers working into the night and at weekends.
"The NUT believes teaching is one of the best professions anyone could hope to do. It is, however, being made a very difficult job under this Government.
"Teachers need to be trusted. They need to have time to have a life outside of work and they need to see an end to the continual blaming and hectoring they get from ministers.
"It is for real reasons that graduates are choosing other professions, and many qualified teachers are leaving or considering leaving. This situation will continue unless these issues are addressed."
Concerns about teacher workload are not new.
A report by the NUT in October 2015 found more than half of its members were considering leaving the profession in the next two years - with workload and the desire for a better work-life balance the two main triggers for quitting.
The survey found that two-fifths (39%) said they suffered low morale, while 53% were considering leaving in the next two years.
A majority (73%) also said they believed current policies for the school curriculum and pupil assessment were "narrow and uncreative".
The union said teachers were working anything up to 60 hours a week.
The Government launched its workload challenge survey in October 2014 to gauge staff satisfaction with the amount of time they were able to spend in the classroom.
Launching the survey, Nick Clegg, the then-deputy prime minister, said teachers ought to be freed from "burdensome workloads".
A Department for Education spokesman said: "It's disappointing to see the NUT taking this approach instead of working constructively with us to ensure their members and teachers across the country deliver our vision for educational excellence everywhere.
"As set out in our White Paper we have a vision to spread educational excellence everywhere and are determined to continue raising the profession's status. It would be refreshing to see the NUT doing likewise."