Educators in informal settings can be a key part of the learning experience, yet they are often poorly supported as professionals. This study followed the professional development of museum educators who participated in iterative implementation of a new school trip program focused on climate change. The learner-centered pedagogy, inquiry format, and controversial content of this program all presented challenges to the educators' existing models of learning and teaching in the museum. We offer four case studies that explore how part-time museum docents engaged in reflective practice through iterative implementation and how their approaches to learning and teaching in the museum changed, or failed to change. Findings have implications for addressing the challenge of effective professional development for informal educators, particularly in content areas that may be scientifically challenging or socially controversial.