Summer vacation exerts a negative effect on children’s (5-12yrs) obesogenic behaviors (i.e., reduced activity, increased screen time, poor diet intake, shifted/disrupted sleep); children gain 3-5 times the amount of weight during the summer compared to the entire school year. The structured days hypothesis posits the structured environment created by school regulates obesogenic behaviors. During summer, less structure is present, leading to accelerated weight gain. We hypothesize seasonal changes in children’s obesogenic behaviors may be due in part to parents relaxing rules/routines related to obesogenic behaviors during the summer. During summer vacation parents are more lenient with rules/routines, such as allowing children to go to bed later and use screens more frequently. However, when a child attends a program that occurs at pre-specified days and times, like school, parents may enforce health-promoting rules/routines (e.g., earlier bedtime, limits on screens). Because the typical operating hours of summer day camps mimic the structure provided by school, attending summer day camp may also influence parent health-promoting rules/routines. This would promote greater consistency of parent health-promoting rules/routines during the summer; similar to rules/routines during the school year. We hypothesize that attending summer day camp will influence parent health-promoting rules/routines in the absence of a formal parenting behavior intervention and lead to more healthful behaviors of children at home. This spillover effect – summer day camp influences parent health-promoting rules/routines at home – can have important implications for obesity interventions during the summer. This F32 Post-Doctoral fellowship application will leverage data from a randomized clinical trial (NIDDK R01DK120490, PI Beets) enrolling 280 elementary-age children from low-income households with half randomized to receive free access to 8-weeks of community-operated summer day camp. We will quantitatively and qualitatively examine the impact of providing access to summer day camp on parent rules/routines associated with sleep, screen time, and diet. Further, we will examine the influence of parent health-promoting rules/routines on objectively measured obesogenic behaviors and child zBMI. The primary aim is to evaluate the impact of access to summer day camp on changes in parent health-promoting rules/routines from school to summer compared to a control group who do not receive free summer day camp. The secondary aim is to evaluate the impact of parent health- promoting rules/routines on changes in child obesogenic behaviors and weight (zBMI) from the school year to summer. The final aim is to describe parent perceptions of how/why they maintain/change health-promoting rules/routines during the summer. This study is significant because it is necessary to understand the mechanisms by which child obesogenic behaviors shift during the summer. This study will inform future...