Highlights• Environmental outcomes reported in 36 US studies of youth inquiry approaches.• Outcomes included changes to practitioners, policies, programs, research, and peer group norms.• Long term, advocacy-oriented groups targeting decision-makers were more likely to report outcomes.Abstract Over the last twenty years, research on the impact of engaging children and adolescents in the generation of new knowledge about their lives, schools, and communities, has grown tremendously. This systematic review summarizes the findings from empirical studies of youth inquiry approaches in the United States, with a focus on their environmental outcomes. Searches of four interdisciplinary databases retrieved a total of 3,724 relevant articles published between 1995 and 2015. Sixty-three distinct studies met the systematic review inclusion criteria, of which, 36 (57.1%) reported that the youth inquiry approach contributed to positive changes among adults, peers, organizations, and/or institutions. These environmental outcomes were qualitatively recorded, inductively categorized, and then organized into Bronfenbrenner's ecological framework. Youth inquiry approaches led to practitioner growth and changes in peer group norms at the micro-system level, program development or improvement and research benefits at the meso-system level, and school, city, and state level policy adoption at the exo-system level. Qualitative methods, especially case studies, were most commonly used to evaluate the impact of youth inquiry approaches on environmental outcomes. Studies of approaches that utilized advocacy to create change, targeted decisionmakers as the audience for the youth's work and convened for a longer duration were more likely to report improved environmental outcomes. This systematic review suggests that youth inquiry approaches are a promising strategy for ecological systems change.