Spending time in nature during childhood can improve mental and physical health, support academic success, and cultivate pro-environmental attitudes and behaviors. Increasing outdoor time during school can enhance the likelihood of those outcomes for all students. However, in practice incorporating outdoor time into the school day can be challenging. This study reports on barriers identified during the development phase of an action research project that aimed to increase outdoor time as a regular, repeated part of the elementary school day. Teachers (n = 22) and administrators (n = 3) in one school district in the Northeastern United States were asked to describe the barriers that limited their opportunities to take students outside. Data indicated 33 discrete barriers and 5 themes that cut across the barriers. Interactions and overlap across barriers increased the challenges encountered by teachers. A systems thinking approach is suggested to increase outdoor time in schools.