Project Summary Schools are critical settings to promote child health, learning, and wellbeing. However, unprecedented declines in state education funding have forced many US school districts to consider cost-cutting measures to alleviate budgetary pressures. Use of the four-day school week (FDSW) as a potential cost-saving strategy has increased 630% in the US over the last two decades despite a significant lack of data on how this strategy impacts child and family health and wellbeing. Losing one day of school per week diminishes exposure to school-day physical activity opportunities, school meal programs, academic instruction, and other support services, which may affect child health behaviors, socioemotional development, mental health, risk behaviors, and educational attainment. Reduced access to school services via FDSWs also may increase childcare needs, which may alter family labor participation decisions and/or impact household resources allocated to food. This proposed R21 study convenes an interdisciplinary team of experts in public health, economics, and Cooperative Extension to generate some of the first evidence of FDSW impacts on child and family outcomes using quantitative and qualitative approaches across two aims. For Aim #1, we will link existing Oregon and national datasets to our proprietary national longitudinal dataset of FDSW use to compare outcomes between four- and five-day school models, including child health behaviors (e.g., diet, physical activity), risk behaviors (e.g., crime, substance use), socioemotional factors, achievement, attendance, graduation/dropout decisions, and physical education exposure and family labor decisions and food security. For Aim #2, we will leverage ongoing partnerships with Oregon schools to conduct focus groups with families in four- and five-day schools to contextualize the FDSW experience of families and to probe the mechanisms underlying Aim #1 findings. Oregon has the fourth highest density of FDSW districts and represents a robust setting to conduct this research. Our central hypothesis is that child and family health and wellbeing will be negatively impacted by FDSW use compared to five-day schools due to reduced exposure to academic instruction and other school- based support services. Our long-term goal is to understand how the school environment impacts child and family health and wellbeing. The objective for this R21 proposal is to provide novel evidence about the impacts of reduced school exposure via FDSWs. To date, there have been two metrics predominantly used to weigh the impacts of adopting a FDSW: cost-effectiveness and academic achievement. Our rationale for undertaking this project is to extend beyond these metrics to provide crucial evidence regarding the potential impacts of FDSW adoption on child and family health and wellbeing to address this significant evidence gap. We expect our estimates of the impacts of FDSW on children and families will change how stakeholders...