Laura Doel, national secretary of school leaders’ union NAHT Cymru, said: “School leaders are doing everything possible to help keep pupils and staff safe, comfortable and able to focus on learning during the current heatwave.

“This includes limiting the time children spent in the sun during breaks, ensuring additional water is available, relaxing uniform policies where appropriate, and ventilating classrooms as best they can.

“However, their task is made harder by a largely outdated school estate which was not designed to cope with the temperature extremes which appear to be becoming the norm.

“While we need the Welsh Government to fix the huge repairs backlog facing schools, and welcomed yesterday’s announcement of an additional £40m for this purpose, it’s vital there is also investment to modernise school buildings to ensure they are conducive to learning all year round in both very hot and very cold weather.

“This could include everything from air conditioning and improved ventilation, to better insulation and solar panels.”

NAHT sent guidance to all its members on dealing with high temperatures yesterday.