Background: Limited physical activity (PA) is a key factor contributing to obesity and independently protects from diseases in youth and later in life. Students spend most of their time in schools sedentary and have limited opportunities to engage in PA. By making changes to the school environment and developing a school culture that actively supports and reinforces PA behavior, Comprehensive School Physical Activity Programs are designed to make PA engagement throughout each school day the accepted social norm. The purpose of this study was to determine the effects of environmental and behavioral modifications to school-level PA participation for girls and boys.

Methods: This study used a hybrid reversal design by alternating baseline phases with two intervention phases that provided increased access and opportunity to PA, and behavioral prompting and reinforcing plus access and opportunity, for all students to engage in PA during lunch. Physical activity and contextual data were collected using a previously validated instrument (System for Observing Play and Leisure Activity in Youth; SOPLAY). Behavioral data were collected using a novel instrument (System for Observing Behavioral Ecology for Youth in Schools; SOBEYS) developed to measure prompting and reinforcement contingencies of PA participation consistent with the Behavioral Ecological Model.

Data Analysis: The number of students engaged in moderate-to-vigorous PA (MVPA) and the proportion of students in MVPA were analyzed using visual analysis of graphic data and general linear statistical models, with environmental and behavioral variables as predictors.

Results: Increases in the number of girls and boys in MVPA were seen visually and statistically during the environmental and the environmental plus behavioral intervention phases compared to baseline. No differences were seen visually or statistically between intervention phases. Intervention effects were larger for boys than girls. The SOBEYS instrument was able to produce valid and reliable data regarding prompting and reinforcement of PA. However, environmental factors appear to have a greater influence on PA than behavioral factors.

Conclusion: Modifying the school environment to increase access and opportunity for PA during lunch can lead to positive changes in MVPA during the school day, with special consideration needed to engage more girls.