In this article, we describe a large-scale data collection effort about the environmental learning field in Maine. This approach utilized a stakeholder engagement process which included over 600 project managers, educators, and school administrators from both formal and informal education settings. Our focus on collecting data about specific environmental learning projects allowed us to analyze alignment with a selection of best practices in environmental education drawn from NAAEE's "K-12 Guidelines for Excellence." We highlight the characteristics of "high-mastery" projects -- those most aligned with the targeted best practices in environmental education -- and describe implications for supporting growth of the environmental learning field in Maine moving forward and equitable access to quality programming for youth.