Fresh school closures loom this autumn as a major teachers' union voted overwhelmingly for walkouts over pay.
In a bitter dispute over pay and working conditions, a staggering 88.5% of eligible members of the NASUWT voted to back strike action.
The union, which has 300,000 members across the UK, failed to meet legal turnout rules earlier this year. But anger at the Government's measly pay offer has pushed its members to back walkouts on a turnout of 51.9%.
The NASUWT said it would begin action short of all-out strikes in September - and full walkouts are on the table.
It comes after leaders of the four major teaching unions agreed earlier this year to coordinate industrial action if their strike ballots are successful.
Members of the National Education Union (NEU), the largest education union, have already taken part in seven national strikes and three regional walkouts in recent months.
The NEU is re-balloting its members to extend its strike mandate for another six months.
School leaders in ASCL and the NAHT unions are also being balloted for walkouts. Deadlines on all three ballots loom at the end of the month.
NASUWT General Secretary Dr Patrick Roach said his members had sent a "strong message" to the Government that "teachers demand a better deal on pay and to address excessive workload and working hours".
He added: “Our members have secured the largest mandate for industrial action by the NASUWT in over a decade, exceeding the Government’s anti-trade union ballot thresholds.
“We have today written to the Government and to employers confirming the prospect for industrial action in schools the length and breadth of the country from this autumn."
The unions have already rejected a £1,000 one-off payment for 2022/23 and an average 4.5% rise for staff next year.
Education Secretary Gillian Keegan kicked the decision to the Government-appointed pay review body, which has reportedly recommended a 6.5% wage hike.
But the Department for Education (DfE) has refused to publish the advice amid mounting speculation ministers could offer less than the amount recommended by pay review bosses.
Dr Roach urged the Government to "stop playing politics" and publish the pay proposals.
He said: "The STRB's recommendation of a 6.5% pay award for teachers and headteachers, which has been widely reported, is the minimum to which our members are entitled. However, NASUWT members are clear that teachers deserve better than just another real terms pay cut.
"The Government is ultimately responsible for teachers' pay and working conditions and ministers must now get back to the negotiating table to agree a deal that will command the support of our members."
Rishi Sunak said that workers needed to be rewarded fairly - but taxpayers would have to "foot the bill for pay rises".
Speaking at the NATO summit in Lithuania: "I think everyone knows the economic context we are in and we need to make sure that Government decisions, particularly when it comes to not borrowing more, are made responsibly so that we don't fuel inflation, make it worse or last for longer."
A DfE spokesperson said: “Further strike action will cause real damage to pupil learning and even more disruption for parents right across the country. Thousands of schools have received significant additional funding as part of the extra £2 billion of investment we are providing both this year and next, which will take school funding to its highest level in history next year.
“We recognise and value the hard work of teachers, but we must balance pay offers with the need to make responsible decisions that are affordable so we can continue to tackle inflation.
“As part of the normal process, the independent School Teachers’ Review Body has submitted its recommendations to government on teacher pay for 2023/24. We will be considering the recommendations and will publish our response in the usual way.”
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