The impact of a yearlong professional development intervention on physical education teachers' psychosocial perceptions was investigated. Experienced mentor teachers (n = 15) were paired with inexperienced protege teachers (n = 15) who helped them learn how to teach a health-related physical education curriculum (i.e., the Exemplary Physical Education Curriculum). Using the theory of planned behavior as the guiding theory, it was hypothesized that teachers would experience favorable increases in various psychological constructs (e.g., attitude) and variables reflecting the social culture of their schools (e.g., administrator's perceptions) as compared with control teachers (n = 17). A variety of statistically significant main and interaction effects with mean scores in expected directions were found. In general, mentors and proteges developed a more positive view of their own psychological state (e.g., perceived behavioral control) and of the immediate school social environment (i.e., support from administrators and fellow teachers). The significant results, combined with meaningful effect sizes, supported the effectiveness of this intervention. (Contains 6 tables.)