While multiple valid measures exist for assessing outcomes of environmental education (EE) programs, the field lacks a comprehensive and logistically feasible common instrument that can apply across diverse programs. We describe a participatory effort for identifying and developing crosscutting outcomes for Environmental Education in the twenty-first Century (EE21). Following extensive input and debate from a wide range of EE providers and researchers, we developed, tested and statistically validated crosscutting scales for measuring consensus-based outcomes for individual participants in youth EE programs using confirmatory factor analysis across six unique sites, including two single-day field trip locations, four multiday residential programs and one science museum in the United States. The results suggest that the scales are valid and reliable for measuring outcomes that many EE programs in the United States can aspire to influence in adolescent participants, ages 10-14.