The purpose of this study was to inquire into the ways in which participation in physical science professional development impacts science teachers' professional learning and ultimately their practice over time. This study strove to provide a greater understanding of teachers' processes as they engage in professional learning and make changes in their practice long after the requirements of the professional development have been met. The six respondents that participated in the inquiry were physical science educators who were teaching in four different high schools in Central California. The guiding research question was stated as: How does participation in physical science professional development impact teachers' professional learning and ultimately their practice? Three sub-questions were also explored: In what ways does physical science professional development impact teachers' pedagogical content knowledge over time? In what ways does physical science professional development impact teachers' curriculum decision-making processes over time? In what ways does physical science professional development support a teacher's professional learning over time? Collective case study methodology was used in order to acquire multiple perspectives on the processes of teachers' professional learning and how professional development experiences have impacted this process. From four cross-case analyses of interviews, classroom observations, and documents, six themes emerged elucidating the process of professional learning. The process of professional learning is "driven" by a "constant desire to learn" resulting in the participation in professional development experiences where "bits-n-pieces" of curriculum are incorporated into the teachers' practice supported by "relationships and reflection". The "pressure to conform to education policy" tempers the entire process of professional learning. Lastly, the process of professional learning has produced teachers as "leaders". Each aspect of the process of professional learning has been impacted by the respondents' participation in professional development. By engaging in the iterative process of professional learning described here, respondents are transforming their professional development experiences in order to learn from and about their practice over extended periods of time. As professional learners, the respondents act as change agents in their own practice, schools and learning communities. Based on the results, implications for practice and recommendations for further inquiry are also presented. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]