Teachers in parts of England and Wales are on strike on Thursday — the third planned day of action demanding higher pay rises as the country is hit by rampant inflation and interest rate rises.
The National Education Union estimates that about 200,000 members will have walked out this week during three days of strike.
On Thursday, it was teachers in Wales and southern England that are on strike. On Tuesday, colleagues in northern England walked out and on Wednesday, teachers in the Midlands and eastern regions went on strike.
The NEU said the “majority of schools” were expected to either restrict access to pupils or fully close.
Picket lines will be mounted outside schools and rallies are due to be held in Cardiff, Chichester, Bristol and Plymouth.
“While no teacher wants to be on strike action we are grateful for the support of parents, and do not take it for granted,” said NEU joint general secretary Mary Bousted.
“Many understand first-hand the issues faced by schools and colleges and their children's teachers.
“They need no persuasion that there is disruption every day of the school year, thanks to the government's poor decision-making and short-sighted policies on education.”
A poll by Ipsos suggests that three in five (60 per cent) parents and guardians support teachers taking strike action, while 43 per cent are worried about their children catching up on work missed because of the walkouts.
Education Secretary Gillian Keegan last week invited the teaching unions to “formal talks on pay, conditions and reform” provided that this week's walkouts were suspended.
Ms Keegan has called the union's decision not to suspend the regional strikes “hugely disappointing”.
Workers in a numbers of sectors, including nurses, paramedics and rail workers, have all held strike action over the last two months, generally in disputes over salary and conditions as pay offers fail to cover inflation.
Further national strikes by NEU members in England and Wales are planned for March 15 and 16.
Dr Bousted said: “We urge Gillian Keegan to start negotiating with the profession to ensure we have a resolution for the sake of teachers and children's education.
“The government's continued stonewalling of talks will not improve their standing among parents and the general public.
“We need to see a substantive offer that will address the issues which are eroding this essential public service.”
The Association of School and College Leaders is the leading professional association for all school and college leaders.
General secretary Geoff Barton said: “This week's rolling series of strikes is posing further challenges for school leaders.
“While they will draw on their experiences from last month's strike, in many cases they will not know the exact number of staff taking part in the strike until the day itself.
“Leaders have been planning provision for students according to expected staffing levels and in many cases this will translate to on-site provision for vulnerable pupils, and as many year groups as can be safely accommodated, with remote learning for others.
“While they are managing the situation as best they can, there will inevitably be disruption to education.”