2024 Yes Stress in School. Some Empirical Hints on the Circadian Cortisol Rhythm of Children in Outdoor and Indoor Classes https://doi.org/10.3390/ijerph14050475 Dettweiler, Ulrich Europe Experimental Students Middle/Jr High (6-8) Green space Stress/Anxiety Stress cortisol Physical activity Outdoor learning mixed effect model Longitudinal study measured diurnal cortisol via saliva in students taught weekly in forest vs. traditional classrooms; outdoor group showed healthier cortisol decline. Suggests nature-based teaching may protect against stress in school environments. 2017