As temperatures in Phoenix soared to 117 degrees Fahrenheit, or 47 degrees Celsius, in July 2026, children living there headed outside to walk to and from school, play during recess and suit up for baseball practice.

These routines have long been part of the school day, but with a rising number of school districts in Arizona, as well as across the country, starting their academic year in mid-July or August, kids are spending more time at school during some of the hottest days of the year.

Heat doesn’t just affect places like Phoenix, which is well known for its scorching temperatures that don’t always drop by much in the evenings.

Many U.S. cities, from Los Angeles to Houston, are oppressively hot when the new school year begins in August or September – and they are only getting warmer. The increased frequency, intensity and duration of extreme heat has become a common concern across many places in the United States and other countries.

We are Arizona State University researchers who study how extreme heat affects children when it comes to their outdoor school activities, physical activity, health and overall well-being.

Our work is part of HeatReady Schools, a program at Arizona State University that helps schools prepare for and mitigate the effects of heat.

We think it’s important to recognize that many schools are underprepared to carry out their days in extreme heat, without the physical infrastructure or planning to keep students and educators comfortable and safe while in the classroom or outside on school grounds.

A problem rising with the heat

The challenge of managing hot school days has intensified, as many U.S. schools have moved the start of the academic year earlier into the summer over the last several years.

School calendar changes are driven by multiple factors, including reducing summer learning........

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