Background: Practical tools are needed that reliably measure the complex physical activity (PA) and nutrition environments of elementary schools that influence children's health and learning behaviors for obesity prevention. The School Physical Activity and Nutrition-Environment Tool (SPAN-ET) was developed and beta tested in 6 rural Oregon elementary schools. Methods: Extension educators were trained to assess elementary school PA and nutrition environments using the SPAN-ET. Two auditors per school worked with school health stakeholders and collected data via document review, interviews, and direct observations. A reliability analysis using percent agreement and kappa statistics was performed to determine consistency between independent auditors. Content analyses of qualitative data were used to triangulate intercoder ratings, verify evidence, and improve reliability. Results: Across the 6 schools, for all 182 measured criteria (PA = 103; nutrition = 79), the percent agreement ranged from 80.8% to 96.8% and kappa from 0.61% to 0.94. Conclusion: The SPAN-ET was a reliable instrument for assessing the quality of elementary school PA and nutrition environments, and a sensitive measure for objectively identifying specific attributes of SPAN-ET areas of interest to target for school environmental and policy improvements aimed at supporting students' obesity preventing behaviors.