Schools have been told they can use volunteers to stay open after teachers voted to strike on seven days between now and mid-March in a row over pay.
Teachers across England and Wales have voted to strike over the next two months amid fears walkouts will lead to a return to online lessons and Covid-style classes.
Nine out of 10 members of the National Education Union (NEU) voted for the action and the union passed the 50 per cent ballot turnout required by law.
The NEU announced there would be seven days of walkouts between now and mid-March, but said any individual school will be affected only on four days.
The Department for Education (DfE) has issued updated guidance for schools.
The guidance calls on headteachers to “take all reasonable steps to keep the school open for as many pupils as possible”.
While the decision to open, restrict attendance or close academy schools lies with the academy trust, the DfE said it is usually delegated to the principal, and the decision for maintained schools rests with the headteacher.
The latest guidance stated: “It is best practice for headteachers to consult governors, parents and the local authority, academy trust or diocesan representative (where appropriate) before deciding whether to close.”
Headteachers are entitled to ask staff whether they intend to strike, the DfE added.
The first day of strikes will be on February 1, when more than 23,000 schools in England and Wales are expected to be affected, the NEU said.
The date is the same day as a “national day of action” that will see rallies across the country and a strike by 100,000 civil servants.
The union is also to target the Budget, on March 15, in a bid to send a message to ministers. Teachers will also hold a rally in Westminster that day, it said.
As well as strike action the union asked all its members to write to their MP – and visit their surgeries – to make the case for an inflation-proof pay rise.
Downing Street had called on the unions to call off any strike.
No 10 said that teachers should not strike and inflict “substantial damage” to children’s education, especially after so many missed out on schooling during the pandemic.
Earlier, Mary Bousted, the leader of the NEU predicted her members would vote to strike, but said it was “highly unlikely” action would take place during exams.
Making the announcement, Ms Bousted and her colleague Kevin Courtney 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.”
Ahead of the strike ballot results, 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.”
Last week, a ballot of members of members of another union, the NASUWT teachers’ union, failed to reach the required 50 per cent turnout threshold, although nine in 10 of those who did vote backed strikes.
Teachers are the latest public sector workers to vote to strike, as the government battles a wave of industrial action which has swept the country for months.
Members of the Royal College of Nursing (RCN) in England will this week walk off wards on Wednesday and Thursday. But the union has warned that if progress is not made in negotiations by the end of January the next set of strikes will include all eligible members in England for the first time.
Mr Sunak has instead that the pay claims of unions are unaffordable and that they will tick to wage rises recommended by pay review bodies.
GMB leaders are also meeting today to decide whether to call more strikes among ambulance staff, because of the lack of progress in talks.
Any decision is likely to be announced later in the week.
