This study evaluated Gregoire’s (2003) Cognitive–Affective Conceptual Change model (CAMCC) for predicting and assessing conceptual change in science teachers engaged in a long-term professional development project. The project was set in a large school district in the southwestern United States. The authors used a multiple case study method with data from three teacher participants to understand the process of integrating and applying a reform message of inquiry based science teaching. Findings show that the CAMCC functioned well in predicting how these teachers made decisions that impacted how they processed the reform message.