More than 300 schools across England and Wales either partially or fully closed because of the hot weather on 24 and 25 June.
Chris Parry, the head teacher of Lewis School in Pengam, said he made the decision to close his school on both days based on risk assessments, building conditions and staff judgment, with older parts of the school particularly hot and poorly ventilated.
He said staff had tried to “mitigate” the heat by keeping pupils hydrated, using shade and keeping children indoors where possible.
However, as conditions worsened and warnings escalated, he and governors acted “with caution” and decided closure was the safest option.
Parry said parents were “really supportive” and pupils were given advice to stay safe and comfortable at home.
He said that while resilience was “really important”, safety must come first, especially for young children in crowded classrooms during extreme heat.
Parry noted that many businesses also closed during the heatwave and said young people should understand workplace responsibilities.
He said schools needed long-term planning and investment, including better cooling systems, adding that he had already spoken with local air conditioning suppliers.
He added that schools, government and local authorities should work together to adapt buildings designed for colder conditions.
“Our job, really, is to develop that resilience with pupils, but also to create that safe and safe environment for them to work in,” he added.
Laura Doel, from National Association of Head Teachers Cymru (NAHT), said school leaders in Wales should “think carefully” about keeping pupils and staff safe during heat, adding that many older school buildings were “ill-equipped to deal with extremes of temperature”.
Describing closures as a “last resort”, she said the government should “act more urgently” to upgrade buildings, adding: “School buildings need to be conducive to learning all year round.”
Claire Armitstead, from the Association of School and College Leaders Cymru (ASCL), said school leaders were “best placed to make decisions around opening and timetabling during periods of extreme weather, based on what is most appropriate in their context”.
However, she said many schools had “poor” ventilation and no air conditioning, so more investment was needed to make buildings safe and suitable in hotter conditions.
The Welsh government said it “continues to work closely” with local authorities to ensure funding arrangements “meet their local needs and priorities”.
It said it had recently announced £40m of funding, external for school maintenance.