How teachers' changes in their science teaching practices unfold over time remains unclear. We need greater understanding of the processes at work in professional development (PD) and how to sustain those processes that are effective over time. Effective PD processes are seen as those that recognize teacher change is "multidimensional"--taking an integrated view of the affective, cognitive, and behavioral aspects of teacher change. In this article, we report on what we learned about the teacher change process during a 2-year preschool PD intervention effort with Head Start teachers that was focused on a science, technology, and engineering curriculum. The present study sought to further address gaps in our understanding of teacher change, by examining in more detail the multidimensional relations among Head Start teachers' beliefs and attitudes toward science teaching and learning (representing the cognitive domain of change) and their science and engineering practices (representing the behavioral domain). Forty-eight teachers (n = 30 Intervention, n = 18 Control) from a large urban Head Start program in the northeastern US participated in this study. Results revealed that teachers' initial attitudes and beliefs had little effect on their science and engineering practices, whereas their science and engineering practices throughout the time of the project had a significant effect on their later attitudes and beliefs. In addition, teachers' science and engineering teaching practices were related to their ratings of children's overall engagement, though their attitudes toward and beliefs about teaching science were not.