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Stress in school. Some empirical hints on the circadian cortisol rhythm of children in outdoor and indoor classes


Participating in outdoor education classes on a regular basis has a positive effect on children’s stress responses

This study was based on the understanding that stress exposure during childhood might lead to a biologically-based susceptibility to stress-related illnesses later in life. This study was also based on the understanding that exposure to green environments can have some positive effects on mental health. The aim of the study was to determine if regular intervals of outdoor education over the course of one school year would have a stress protective effect on the students.

Forty-eight students (age 11) from the same school in Heidelberg, Germany participated in the study: 37 in an intervention group; 11 in a control group. Students were not randomly assigned to group. The intervention group participated in learning activities in a forest setting one full day per week throughout the school year. The control group participated in a traditional class without outdoor teaching. Stress level and physical activity (PA) data were collected on both groups at three different times throughout the year (fall, winter, and spring). Stress levels were measured via three cortisol saliva samples per day. Normal cortisol levels are high in the morning and decrease throughout the day. Previous research indicates that cortisol is a fitting measure for stress with respect to mental health. Previous research also indicates that PA levels are higher in outdoor education settings compared to indoor settings. Since high PA can lead to higher cortisol levels, this study factored in PA data as a possible influence on the cortisol scores.

As expected, the children in the outdoor classes showed higher levels of PA than the children in the traditional classes. The difference was especially higher in the second half of the school day. Overall, the accumulated time in moderate-to-vigorous PA for the intervention group was more than twice as much as the control group. Students participating in the forest class showed a steady decline of cortisol during the school day. This decline was not observable in the control group. These cortisol readings were constant over the school year. Of concern is the fact that the cortisol profile of students in the indoor class was similar to profiles of individuals prone to develop a stress-associated mental disorder, such as depression. Further data analysis indicated that differences in PA did not account for the differences in cortisol levels of the two groups. Therefore, differences in PA and cortisol levels could be attributed to the specific environment of the students.

These findings indicate that outdoor education had a positive effect on the stress responses in children. These findings also support the idea that outdoor education over regular intervals is beneficial to children’s mental and physical health. The authors call for further research to better understand the impact of outdoor education on children’s mental health, especially in relation to stress.


Dettweiler, U., Becker, C., Auestad, B.H., Simon, P., Kirsch, P., (2017). Stress in school. Some empirical hints on the circadian cortisol rhythm of children in outdoor and indoor classes. International Journal of Environmental Research and Public Health, 14(5)


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