Teachers in England and Wales have voted in favour of strikes in a dispute over pay.
Nine out of 10 teacher members of the National Education Union (NEU) voted for strike action and the union passed the 50% ballot turnout required by law.
The union has declared seven days of walkouts in February and March, but it has said any individual school will only be affected by four of the days.
The NEU’s Kevin Courtney described the outcome in England as “the biggest ballot result of any union in recent times”.
The first day of strikes will be on February 1 and more than 23,000 schools in England and Wales are expected to be affected, the NEU has said.
School leaders in Wales are also set to take industrial action over pay, but heads in England will not stage strikes after the National Association of Head Teachers (NAHT) ballot turnout failed to meet the legal threshold.
In England, 90% of NEU teacher members who voted in the ballot backed strikes, with a turnout of 53%.
In Wales, 92% of NEU teacher members who voted in the ballot backed strikes, with a turnout of 58%.
Overall, 300,000 teachers and support staff in England and Wales were asked to vote in the NEU ballot.
Support staff in schools in Wales are also set to go on strike in the dispute over pay after 88% of balloted members backed action, with a turnout of 51%.
However, the NEU’s ballot of support staff in schools and sixth-form colleges in England did not achieve the 50% ballot turnout required by law for action.
The result from the NEU, the largest education union in the UK, comes after a ballot of members of the NASUWT teachers’ union last week failed to reach the 50% turnout threshold.
The NASUWT said it will continue its campaign on pay and expects to announce plans “shortly” for further balloting of members.
On Monday, the NAHT revealed that 87% of members in England taking part in the union’s pay ballot voted in favour of action short of strikes, while 64% supported strikes.
But the turnout was 42%, which is below the threshold required by law.
The NAHT has said it is considering re-running its industrial action ballot in England due to concern that the democratic process has been compromised amid postal disruption.
In Wales, 95% of members taking part in the school leaders’ union NAHT Cyrmu ballot backed action short of strikes and 75% supported strikes, with a turnout of 55%.
The Department for Education (DfE) has offered a 5% pay rise to most teachers for the current school year, but the NEU is demanding a fully-funded above inflation pay rise for teachers.
The NEU said the vote shows teachers are not prepared to “stand by” and see the education service “sacrificed” due to “a toxic mix of low pay and excessive workload”.
Mary Bousted and Mr Courtney, joint NEU general secretaries, said: “We have continually raised our concerns with successive education secretaries about teacher and support staff pay, and its funding in schools and colleges, but instead of seeking to resolve the issue they have sat on their hands.
“It is disappointing that the Government prefers to talk about yet more draconian anti-strike legislation, rather than work with us to address the causes of strike action.”
The union leaders added that historic real-terms pay cuts for teachers had created an “unsustainable situation” amid a cost-of-living crisis, adding that staff were leaving the profession “in droves”.
“This is a scandalous waste of talent and taxpayers’ money, yet the Government seems unbothered about the conditions they are allowing schools and colleges to slide into,” they said.
Dr Bousted and Mr Courtney added: “It continues to be the aspiration of the NEU and its membership that this dispute can be resolved without recourse to strike action.
“We regret having to take strike action, and are willing to enter into negotiations at any time, any place, but this situation cannot go on.”
Dr Bousted told an online briefing announcing the ballot results that the NEU will meet with Ms Keegan on Wednesday and will have “strength in the negotiations” after the vote.
She said: “They (the Government) know that we mean business. They know that you are prepared to take action to protect your jobs, to protect your pay and costs, and to protect your ability to remain in the profession.
Ms Keegan has called the strike vote “deeply disappointing” and argued it “will have a damaging impact on pupils’ education and wellbeing”.
But Dr Bousted insisted strike action is “absolutely not designed” to hurt or disadvantage pupils or parents.
The NEU said teachers in sixth-form colleges in England, who have already been balloted and been on strike in recent months, will also take part in action on the strike days between February 1 and March 16.
Ahead of the strike ballot results on Monday, Downing Street urged teachers not to strike and inflict “substantial damage” to children’s education.
The Prime Minister’s official spokesman said: “We would continue to call on teachers not to strike given we know what substantial damage was caused to children’s education during the pandemic and it’s certainly not something we want to see repeated.
“We would hope they would continue to discuss with us their concerns rather than withdraw education from children.”
The DfE issued updated guidance to say agency staff and volunteers could be used to cover classes on strike days, with schools expected to remain open where possible, although remote learning is also an option and the most vulnerable pupils are to be given priority.
Last week, schools across Scotland were shut as members of the Educational Institute of Scotland (EIS), NASUWT, Scottish Secondary Teachers’ Association (SSTA) and AHDS took strike action.
Schoolchildren in Scotland will miss more lessons this week as members of the EIS are beginning 16 days of rolling strike action on Monday.
The wave of industrial action will continue this week with members of the Royal College of Nursing (RCN) in England due to walk out on Wednesday and Thursday.
The RCN announced on Monday that it will stage two more strikes in England and Wales on February 6 and 7, with more NHS trusts taking part than during two days of strikes in December.