Place-based Ecology Education (PBEE) has emerged as a compelling approach to achieving the sustainability goals of Environmental Education (EE), including helping children understand, care about, and take action to protect the environment. Collaboration for teacher training can amplify and expand the reach and effectiveness of PBEE within a given geographic region. This case study of a collaborative of five PBEE professional development organizations provided a noteworthy example of collective evaluation. The primary data source was quantitative and qualitative analysis of 156 survey responses from K-12 classroom teachers, administered from 2016 to 2018 in the Upper Valley region of New Hampshire and Vermont. On average, teachers reported medium-sized (Cohen’s was 0.4 to 0.6), statistically significant changes over the prior year for all six PBEE core practices measured. Teacher responses to open-ended survey items suggested that PBEE often involves coordination between and contribution from multiple players with different roles but similar goals. Cross tabulation with quantitative results suggested that collaboration within schools was a central factor associated with high levels of PBEE practice.