The authors examined teachers' beliefs and classroom practices during a 2-year professional development program that required middle-school teachers to develop, implement, and revise problem-based, interdisciplinary curricula focusing on locally relevant environmental health issues. The results of the study indicate that over the course of the program, teachers' self-efficacy, beliefs about the classroom learning environment, and reported use of reform-based classroom practices increased significantly. The results also indicate that teachers' beliefs about the likelihood of support from the school environment declined significantly, and their outcome expectancy beliefs did not change significantly. The authors offer related data showing the impact of the program on other teacher and student outcomes and advocate for the use of problem-based learning curricula that use local environmental health science issues as an integrative context. (Contains 1 figure, 1 table and 1 note.)