The norm in most American high schools is for subjects of study to be taught independent of each other where students experience a school day with six or more discrete class periods. A review of the literature points to the benefits of interdisciplinary teaching and learning for teachers and students. One of these benefits for teachers is professional growth through interdisciplinary collaboration and in particular growth in interdisciplinary pedagogical content knowledge (IPCK). Recognizing this benefit, educators are attempting to break the siloed nature of disciplines and engage in interdisciplinary teaching and learning. Three case studies of three interdisciplinary projects were constructed. Each case study had two or more high school teachers with at least one teacher in the sciences. The case studies used initial and final interviews, planning meeting observations, and project documents to examine the trajectory of teacher’s IPCK and the patterns of discourse that contributed to the development of IPCK. The data was analyzed using a conceptual framework to look at indicators of IPCK and the contribution of teacher discourse to IPCK. A cross case analysis of the three cases looked for themes and patterns across the cases. Results from this multiple case study showed that indicators of IPCK were present. By maintaining a learner stance, taking on different roles, and engaging in student-centered and action-oriented discourse, teachers opened opportunities for developing IPCK. This study provides educational leaders with a better understanding of how teachers develop IPCK and suggests ways to support this professional growth.