This week’s soaring summer temperatures have put a spotlight on our schools and their ability to cope, with one in Hertfordshire telling me that it recorded temperatures of more than 40C. So why are our schools struggling?

Modern schools often have too much glass, and not enough shading or ventilation to keep out the sun’s heat. During the 1950s, the focus on public health (after the creation of the NHS in 1948) meant that schools were designed to bring in more natural light. Windows often have built-in restrictors that stop them being opened too far, or at all, because of student safety concerns. Some schools have glass atriums, which were a common feature of those constructed during the government’s Building Schools for the Future programme in the early 2000s, but which now give the effect of walking into a Kew hothouse.

Many Victorian school buildings are overheating – not because they were badly designed, but because we have stripped away the features that once kept them cool. These schools were originally designed with passive cooling and cross ventilation in mind, with tall sash windows that could be opened at the top and bottom, allowing warm air out while drawing cooler air in. External shutters and awnings also helped to keep students comfortable during hot weather. But these have mostly gone, thanks to enthusiastic refurbishment, changing safety requirements – or simply because windows have been painted shut.

Now, large expanses of glazing can turn classrooms into hotspots, a problem made worse by single glazing, which lets up to 37% more heat into a building than double glazing. Add to this outdated heating systems and poorly insulated hot-water pipes that radiate heat into classrooms, and you have schools that are becoming heat traps.

But it’s not just indoor spaces that struggle to stay cool. Playgrounds, the majority covered in tarmac and devoid of trees, function as giant outdoor radiators, absorbing heat all day and retaining it in places where children learn and play. Hard playgrounds’ dark surfaces absorb heat instead of reflecting it and can reach temperatures of up to 60C during heatwaves, according to our own research at a school in Catford, south London, making outdoor play uncomfortable and sometimes unsafe.

The scale of this challenge is clear. I run a non-profit community interest company, Retrofit Action for Tomorrow, which helps schools and communities adapt to climate change. During our recent engagements with 80 schools across England, 68% reported experiencing overheating, with more than a quarter describing it as “significant”. Teachers tell us about pupils fainting or vomiting in class due to the heat, and we hear regularly of schools closing, exams being cancelled and vital study time being missed. This is a critical safeguarding issue, and our schools are now on the frontline of the climate resilience challenge. Add to this that heat can cause negative impact on learning outcomes, by increasing task-completion time and errors, reducing cognitive performance and harming test results.

Overheating is only one of the climate challenges facing schools: they will also have to contend with flooding, water scarcity and more frequent extreme weather events over the next decade.

Quick fixes are possible, such as shading rooms by putting pieces of fabric on window exteriors – twice as effective as internal shading – or even coating the glass with yoghurt. Guidance is readily available on when to open and close windows and blinds during hot weather to keep the heat out. When it’s hotter outside than inside, it’s better to close windows and blinds (you can still open windows intermittently for “fresh air”). When outdoor temperatures are cooler – generally overnight and in the morning – you should open windows to get rid of any heat accumulated during the day. At night-time, high-level windows can be opened to allow hot air out, a technique known as “stack ventilation”. To allow “cross ventilation”, open windows on opposite sides of a building and also open internal doors, to create a path to draw cool air in and push warm air out.

Schools that invest in planting and passive cooling measures in outdoor spaces are also seeing benefits: at Dalmain primary school in Lewisham, south London, solar shading, rain gardens and outdoor learning spaces have kept staff and children comfortable during hot weather. Pupils have celebrated the return of butterflies, bees and other insects, reminding us that climate adaptation and biodiversity can work hand in hand to improve children’s emotional, mental and physical wellbeing.

But the challenge is bigger than these tactical interventions: we need investment and collaborative action at a national scale, guided by a clear plan prioritising issues such as those mentioned above. The Department for Education’s new 10-year modernisation strategy signals a shift towards creating more resilient learning environments through retrofit and estate improvement. We hope this means that schools can keep adapting to provide healthy, safe and productive spaces for our children to learn and thrive.

• Harry Paticas is an architect and the founder of Retrofit Action for Tomorrow