Despite increasing attention to the potential benefits of infusing computational thinking into content area classrooms, more research is needed to examine how teachers integrate disciplinary content and CT as part of their pedagogical practices. This study traces how middle and high school teachers (n = 24) drew on their existing knowledge and their experiences in a STEM professional development program to infuse CT into their teaching. Our work is grounded in theories of TPACK and TPACK-CT, which leverage teachers' knowledge of technology for computational thinking (CT), CT as a disciplinary pedagogical practice, and STEM content knowledge. Findings identify three key pedagogical supports that teachers utilized and transformed as they taught CT-infused lessons (articulating a key purpose for CT infusion, scaffolding, and collaborative contexts), as well as barriers that caused teachers to adapt or abandon their lessons. Implications include suggestions for future research on CT infusion into secondary classrooms, as well as broader recommendations to support teachers in applying STEM professional development content to classroom practice.