Children playing outdoors during school recess. Credit: Arizona State University Heat Futures Lab
Heat Didn’t Stop Arizona Students From Playing Hard at Recess
In A Nutshell
- Phoenix-area fourth and fifth graders reported more hard recess play on days above 100 degrees than on days below 95.
- Reported activity held steady for six weeks, even as kids said they felt hot.
- Kids rated their heat after recess, so exertion may explain the link, and cause is unproven.
- Researchers say schools should rely on shade, water, and schedule changes.
Fourth and fifth graders in the Phoenix area did not back off at recess when temperatures climbed past 100 degrees. In surveys filled out right after recess, reports of hard, breathless play rose from 12.5% of responses on days below 95 degrees to 36.4% on days above 100. Rising heat did not slow these kids down, a result that raises a safety question for schools in hot regions.
In the study, published in PLOS Global Public Health, researchers collected data during the first six weeks of the 2024-2025 school year. That stretch overlapped with Phoenix’s hottest September and hottest year at the time, plus its longest run of days at or above 100 degrees on record. Recess is often the main chance for free play during the school day, and in earlier research on 91-to-109-degree days, 60% of observed recess periods at Arizona elementary schools were still held outdoors.
One caution comes first. Students rated how hot they felt only after recess ended, so running hard may have made them feel hotter, rather than heat pushing them to play harder. Researchers stress that the results show a link, not a cause. A kid who just sprinted around the yard will naturally rate the heat higher, whether or not the heat made that child run.
Harder Recess Play Rose With Heat in Phoenix Schools
Schools were randomly selected from a list of 57 Phoenix-area schools that had earlier said heat affected their recess. Principals at five schools agreed to join, and four made the final analysis. On Tuesdays and Thursdays from August 1 through September 11, 2024, fourth and fifth graders filled out a short paper survey right after lunch recess. Parents could opt their children out, and none did.
Students answered two questions. One asked how hard they had been breathing (not at all, a little, or a lot), a stand-in for effort. The other asked how hot they felt: “not at all hot,” “a little hot,” or “a lot hot.” In all, 170 students completed 981 surveys, between two and 11 each. Air temperatures from nearby weather stations were matched to each recess, ranging from 90 to 108 degrees and averaging about 98. Recess ran 15 to 30 minutes of free play, and shade covered anywhere from 13.5% to 53.9% of the schoolyards, a big difference in how hot a yard can feel.
In 35% of surveys, students said most of recess was spent sitting still, 43% said light activity, and 23% said hard play. Nearly half of responses, 45%, reported the highest heat level.
Students who felt a little or a lot hot reported more active play than those who felt not at all hot. Measured temperature told the same story. Hard play was reported in 21.2% of surveys on days between 95 and 100 degrees, landing between the cooler and hotter extremes. Only 32 surveys came from days below 95 degrees, so the cooler comparison rests on limited data.
Activity also held steady across the six weeks, with no drop-off as hot days piled up. Kids’ heat ratings generally tracked the weather, too, so they seemed well aware it was hot.
Hard Play Held Up Where Earlier Studies Expected a Drop
A Texas study found hard play dropped and shade-seeking rose above about 91 degrees. In Phoenix, hard play stayed at levels similar to those measured in earlier studies at around 86 degrees.
Researchers offered two possible reasons. Recess may be such a rare chance to run around after long stretches sitting in cool indoor spaces that the pull to play outweighs the discomfort. Younger children, ages 9 to 11 here, may also have trouble recognizing heat as a reason to slow down. Kids absorbed in a game might simply not notice the heat until they stop, an idea the study did not test.
Risk from a short recess is also unsettled. At 15 to 30 minutes, outdoor play may be too brief to raise the chance of heat illness much, and the authors note that most healthy children can safely play in a wide range of hot conditions when hydration and recovery are adequately maintained.
Schools Cannot Rely on Kids to Ease Up at Recess in Extreme Heat
Researchers pointed to existing plans, including guidance from the Arizona Department of Health Services and California’s Extreme Heat Action Plan, that put adult-controlled protections such as shade, water access, and schedule flexibility ahead of a child’s own judgment. The authors describe “a potential mismatch between behavior and heat-related risk.” Earlier research in Maricopa County, which includes Phoenix, found that schools within the same district handled hot-day recess very differently. The authors stopped short of naming a temperature at which recess should change, saying firmer guidance needs more evidence.
These fourth and fifth graders felt the heat and kept playing hard. Whether heat drove that effort or the effort drove the heat, the takeaway for schools holds: shade, water, and schedule changes belong in place ahead of the hottest days, because a fourth grader’s judgment at recess is not a safety plan.
Paper Notes
Limitations
Because students rated their heat right after recess, those answers may reflect how exertion made them feel rather than heat shaping their behavior, and the design cannot show cause and effect. Activity was self-reported through a breathing question rather than tracked with devices, and the heat question was developed by the research team without formal pilot testing. Data came from one unusually hot season, with temperatures consistently high and narrowly spread, and no comparison data from milder weather at these schools. Humidity, wind, sun exposure, shade use, water access, and hydration were not measured. School differences in recess length, shade, and surface were described but left out of the activity models, and the study did not assess how much each child enjoys outdoor play to begin with. Finally, the work took place in a hot, dry desert climate, so results may not carry over to humid regions where the same air temperature can feel different.
Funding and Disclosures
Support came from the 2023 Heat and Health CHS Pilot Grant Initiative at Arizona State University, which covered recruitment incentives, materials, and supplies but no salaries. Kylie Wilson received salary support during part of the work from the University of Arizona Cancer Center Office of Cancer Research Training & Education Coordination. Allison Poulos and Jennifer Vanos received salary support from the National Science Foundation, and Chris C. Lim from the National Institute of Environmental Health Sciences at the National Institutes of Health. The funders had no role in study design, data collection and analysis, the decision to publish, or preparation of the manuscript. The authors declared no competing interests. Teachers received $25 gift cards for administering the surveys, and each school was offered a $500 recess equipment bundle for taking part, which the paper says was not tied to enrollment, response rates, or activity levels.
Publication Details
Titled “Children’s physical activity during six weeks of school recess in hot weather: Associations with perceived and measured heat,” the study was written by Kylie Wilson (University of Arizona Cancer Center), Jennifer Vanos (Arizona State University School of Sustainability), Chris C. Lim (University of Arizona Zuckerman College of Public Health and Arizona State University School of Technology for Public Health), and Allison Poulos (Arizona State University College of Health Solutions). It appeared in PLOS Global Public Health on November 11, 2026 (volume 6, issue 11, article e0007432) as an open access article under a Creative Commons Attribution License. DOI: https://doi.org/10.1371/journal.pgph.0007432
