Labour has opened the door to changing school hours after more than 2,400 fully or partially closed during the heatwave.Bridget Phillipson earlier today called the extreme heat 'deeply concerning' and said the make-up of the term timetable needed to be kept 'under review'. The National Education Union, Britain's largest education union, however, has blamed this week's closures on successive governments failing to invest in the UK's school estate. It said the government would not fulfil its pledge to make schools fit for purpose until 2246 on its current trajectory and demanded air conditioning be rolled out now.In a letter to Ms Phillipson, General secretary Daniel Kebede said: 'Air conditioning now needs to be rolled out to schools to deal with the health risks associated with extreme heat events. 'We would urge you to set out a timetable for ensuring that schools have this protection, prioritising schools with the greatest need.'Fundraisers have even been launched to buy air conditioning units and fans for schools - with one parent teacher association raising more than £3,500 in 16 hours. On Wednesday, Ms Phillipson urged parents to send children to school if they remain open, saying: 'Pack a water bottle, put on the sunscreen, and trust that your child's school has got this.' Harris Primary Academy Mayflower in Chafford Hundred yesterday, which has stayed open Pupils eat ice lollies in maths class at Harris Academy Primary Mayflower in Chafford HundredBut in a mixed picture across the UK, headteachers have either closed completely, sent children home early or made other adjustments such as relaxing uniform rules. Some teachers have made early collections optional, with provisions made for students who cannot work at home or whose parents cannot collect them early. The measures have infuriated some parents who have been left to juggle child care alongside work commitments as classrooms shut. Mother-of-two Amy Rankin is a full-time carer for her brother. Her son's school is shutting early, but her daughter's is remaining open and has ordered gazebos for children to shelter under. She told the Mirror: 'I understand for a non-working parent they might be able to take their kids to a lido for the day, but for parents who actually have things to do during the day it's not really feasible is it?'We have enough half terms so I am sure the kids would survive a couple of days with a bit of hot weather. 'There would have to be a bomb scare for me to not send my kids to school. We get penalised as parents if we take them out of school for a holiday.'Former TOWIE star and mother-of-one Lydia Bright called the school closures 'madness'. She wrote on Instagram that her daughter's school was closing early for three consecutive days, but said: 'I'm struggling to get my head around it. Children all over the world sit in classrooms in these temperatures every day, without air conditioning.' The reality TV star added: 'Our children happily spend entire days on holiday in this heat and when we collect them at 1pm we're taking them home to houses that are exactly the same temperature.'Maybe I'm missing something? I'm currently overseas trying to rearrange plans for Loretta and I know I won't be the only working parent trying to move schedules and commitments.'Some parents whose children have had classes cancelled have been left furious - calling for a change in attitudes towards pupils, who would be safer at school.Broadcaster James Hanson told LBC: 'We can all feel it, it is very warm and you need to take sensible precautions. But surely one of the lessons we learned during Covid was that maybe shutting schools isn't always in the best interests of the kids.'What is the difference between a child sweltering in their bedroom and a child sweltering in a classroom? Surely it's better for them to be in a classroom under adult supervision where there's a teacher making sure they are drinking enough water.'Surely that is a far more sensible approach… Why are we raising a generation that have been mollycoddled – it's not their fault, it's the parents, it's our fault - we need to change it.'Former Brexit Party MEP Annunziata Rees-Mogg posted the weather forecast on X and wrote: 'They've closed schools for this? It looks like, er, decent weather in late June. Summer does happen every year. Some summers are hotter than others.'Author and political commentator Emma Woolf also tweeted: 'Why are schools pretending these 'extreme heat' closures are about 'safety'? Pupils take part in water play at Harris Academy Primary Mayflower in Chafford Hundred Pupils watch ducklings swim in a tub of water at Harris Academy Primary Mayflower 'For many children school is the safest place to be. Rich families with big houses, leafy gardens, paddling pools are fine but what about poorer kids who live in high-rise flats, no A/C or outdoor space?'It comes as forecasters said temperatures could hit 40C today, with a red warning from the Met Office for extreme heat covering an area stretching from London to Swansea and Somerset to Birmingham, as well as in Brighton, Portsmouth and Southampton. The warning will also run into tomorrow for the South East.Ms Phillipson said: 'I know hot weather can be a struggle. But my message to families is simple: if your child's school is open, you should keep sending them into school.'Teachers are relaxing uniform rules, keeping classrooms cool, making sure children are hydrated, teaching critical skills like water safety, and avoiding vigorous activity on the hottest days. If your child has medical needs which mean you're especially worried about the heat, talk to your school about what they can do.'Every day of absence and lesson missed has a cost – and that cost falls hardest on our most disadvantaged pupils and working class communities. So, pack a water bottle, put on the sunscreen, and trust that your child's school has got this.'Ms Phillipson was also asked on BBC Radio 4's Today programme whether she was considering changing the hours of the school day or time of the school year to avoid the heat.She said: 'I think we need to keep all of that under review as we see how things change and the kinds of extreme of temperature we're seeing are deeply concerning.'But we need to be led by the evidence around all of that and it's just really important that these children are in school.'During a visit to Beanfield Primary School in Corby, Northamptonshire, today, Ms Phillipson also said: 'Schools have had a difficult time of it in that we saw a huge backlog building up over many many years, schools crumbling, we had the Raac (reinforced autoclaved aerated concrete) crisis.'There's been a big job of work left in order to really make sure that all our schools are modern buildings that are able to deliver a brilliant education for our children.'We are investing a lot of money in making that a reality, but I think the challenges that schools are facing around the extreme weather at the moment demonstrate that there's more to do.'The Government allocated £2.4billion in 2025/26 to improve the condition of the school and college estate.Most schools in Spain shift to a half-day in June and September to avoid the afternoon heat.Spain, Greece and Italy also break for the holidays in mid-June, earlier than schools in European countries further north.In England, more than 100 schools were at least partly closed today in Bristol, Gloucestershire, Oxfordshire, Buckinghamshire and Hampshire.In Somerset, more than 200 schools were shut or operating on more limited opening hours.Pupils will also either not be able to attend school or head home earlier than usual at settings in London, Essex, East Sussex, West Berkshire, Devon, Worcestershire and Herefordshire.One school which has remained open is Harris Primary Academy Mayflower in Chafford Hundred, Essex, where children have been sucking on ice lollies during lessons and splashing about in paddling pools to cool down.'I feel more cool and airy,' Advikhaa, 11, said of the special measures, which also include allowing children to swap their school uniforms for lighter clothing.Many schools have explicitly cited red weather warnings and extreme heat for the reasons behind closures, with some explaining classrooms lack air conditioning and that travel to and from school could be risky in the high temperatures.Parkfield School in Taunton said: 'Such exceptionally high temperatures present significant challenges in maintaining a safe and comfortable learning environment, particularly during the hottest parts of the day.'Despite exploring all available options to remain open safely, we believe that the anticipated conditions will make it increasingly difficult to ensure the wellbeing, comfort and safety of both pupils and staff throughout the school day.'While every school must make decisions based on its own circumstances, we believe that closing for these two days is the most responsible course of action.'One parent teacher association has raised more than £3,500 in 16 hours to buy portable air conditioning units, fans and playground gazebos for Dulwich Hamlet Junior School in south London.The organisers said: 'This is an urgent and unbudgeted expense that would have an immediate impact and improve the learning environment in the summers to come.'Extend Learning Academies Network, which runs nine primary schools across north Somerset, said in a letter to parents and carers that the schools will be closed all day today 'due to the forecast severe heat'. Pupils eat ice lollies in maths class at Harris Academy Primary Mayflower in Chafford Hundred Pupils take part in water play at the Harris Academy Primary Mayflower in Chafford Hundred'The safety of our pupils, staff and families remains our top priority,' the trust added.'We understand that these closures may cause inconvenience, but this decision has been made to ensure the wellbeing of everyone in our school community.'Wessex Learning Trust, which runs 23 academies in the South West, announced in a post on Instagram that schools will be closed today 'to keep children, families and staff safe'.The trust said pupils will receive work during the closure period and families will be contacted about any trips, visits or events that may be affected.Wyvern College in Eastleigh, Hampshire, which was closed today, said its leavers assembly and prom will take place with adjustments for heat.Meanwhile, more than 11,500 people have signed an online petition calling for a maximum temperature at which schools can remain open to be established.London Mayor Sadiq Khan called for similar measures to cover workplaces.Speaking at The Aldgate School, he said: 'What used to be a once-in-a-generation occurrence, events of biblical proportions, now take place every year, whether it's heatwaves [or] flash flooding. We haven't adapted.'Sir Keir Starmer said schools have to decide for themselves whether it is right to close early as a result of the heatwave.Asked if it was right that children's education suffer because of the extreme weather, the Prime Minister said: 'It is very hot, and obviously schools will have to take the appropriate measures, and each school will gage for themselves the measures that are appropriate.'But it is important that we as a Government co-ordinate this across the country, and actually with all of the countries within the United Kingdom, which is what we're doing.'Cobra meetings are taking place 'at the official level', Sir Keir said, adding: 'Obviously it falls to me and others to say, take care, be sensible with precautions, and schools are going to have to decide. They are deciding.'Unions have been urging schools to take action during the heatwave.Stacey Booth, GMB national officer, said: 'No pupil or member of staff should be expected to learn or work in unsafe levels of heat.'Once temperatures exceed 30C, schools should act quickly, use the cooler parts of the building, reduce physical demands, increase water breaks and make sensible adjustments to uniform and duties.'These are practical steps that can make a real difference. If they can't be done, school leaders should consider closing parts of the schools.'School leaders' union NAHT and teachers' union NASUWT have called for school buildings to be modernised and a legally enforceable maximum classroom temperature to be set.NAHT general secretary Paul Whiteman said: 'As temperatures continue to rise, school leaders will be thinking carefully about how to keep pupils and staff safe and as comfortable as possible.'While there is no legal 'upper limit' for temperature in schools, they will certainly be doing all they can to mitigate the effects of such high temperatures.'For most, this will mean making straightforward adjustments such as limiting the time spent in the sun during breaks, ensuring additional water is available, making adjustments to uniform expectations where appropriate, and ventilating classrooms as best they can.'If, as it appears, warmer summers are going to become the norm, then Government really does need to act more urgently to improve and modernise school buildings, including a focus on ventilation and potentially air conditioning.'Teachers' union NASUWT said a legally enforceable maximum classroom temperature should be introduced.General secretary Matt Wrack said: 'Teachers have told us that extremes of temperature in their classrooms are their biggest concern about their school building. This affects pupils' ability to learn and teachers' ability to teach.'We believe that a legally enforceable maximum classroom temperature should be introduced, along with investment in greater ventilation, insulation, shaded areas and flood defences in and around schools and colleges in order to make them better equipped to withstand a changing climate and hotter, more intense weather.'NASUWT said several of its members passed out in class on Tuesday when temperatures rose to 40C in certain classrooms particularly exposed to the sun.Mr Bates, the union's national lead for health and safety, said: 'Schools are simply not equipped to deal with these kinds of temperatures.'Daniel Kebede, general secretary of the National Education Union, said: 'Teaching and learning becomes increasingly challenging as temperatures rise to extremes not previously experienced, which is why we recommend that schools should aim to keep indoor temperatures at a maximum of 26C. 'Schools will always be as creative as possible in taking all possible measures to keep children and staff comfortable and safe, but in some schools, and some parts of the country, this will be much more difficult. 'This is why we call upon the government to urgently invest in making all our schools resilient to this type of extreme weather which is only going to become more common.'He said the increase in expenditure on the school estate through last year's spending review was welcome but the current rate of progress will mean it will take 220 years to refurbish all schools.'I know you will share my view that children suffer most when these failing buildings force schools to shut down, particularly disadvantaged children living in deprived, urban areas,' Mr Kebede continued.'For a child living in a high-rise tower block with no private garden or safe green space, the school environment is a vital lifeline. It is not just a place of learning, it is often their only consistent access to open air, physical exercise, and a safe outdoor environment.'Without more investment we can expect more disruption to pupils' learning. This will be worrying to teachers, parents and students. These concerns will only intensify with more frequent and intense heat waves.'The Department for Education said it does not normally advise schools to close during hot weather because attendance is 'the best way for pupils to learn and reach their potential', but that school leaders should ensure they take 'any steps necessary to make sure children are safe and comfortable', as it laid out guidance on how to keep pupils safe.In France, Education Minister Edouard Geffray said that 13,500 schools were closed or placed on special schedules today due to the heat.