The purpose of this study was to explore and identify the experiences that informed the development of three veteran (15+ years of teaching experience) 9th grade physics teachers' specialized knowledge, or PCK, for using representations to teach the topics of energy transformation and transfer. Through the lens of phenomenography, the study was guided by the assumption that there are a limited number of experiences in which teachers engage throughout their career that contribute in significant ways to the development of their knowledge. The primary sources of data were observations of an entire unit of instruction on energy and a series of four stimulated-recall interviews throughout the unit of instruction. The stimulated recall interviews focused on the participants' instruction and knowledge regarding the representations used throughout the energy unit. These data sources were supported by interviews focused on the participants' work history and professional development as well interviews focused on their unit/lesson plans. The results of the phenomenographic analysis revealed that nine categories of experiences informed the development of the three participant's PCK for using representations to teach the energy topics. The categories included: 1) teaching experience, 2) Physics First professional development, 3) other school district-supported professional development 4) collaboration with current colleagues, 5) past collaboration with experienced teachers, 6) academic experiences as a learner of science, 7) school district expectations, 8) collaboration with university faculty and other university professional development, and 9) non-academic life experiences. The analysis also revealed that as a result of engaging in the nine experiences, the participants developed more integrated knowledge for using representations in their instruction, which included understandings regarding the essential features of specific representations, knowledge of barriers to student learning regarding representations, and knowledge of how to help students develop understandings about specific representations. The results of the study highlight that the development of PCK for using representations to teach topics in energy is best supported through a combination of reflection on teaching experience, collaboration with colleagues, and professional development that provides topic-specific instruction in terms of content and pedagogy. These findings have implications for pre-service teacher preparation programs as well as in-service teacher professional development. [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.]