This study examines the effects of a professional development program (TEC) on science teachers’ development of technology, pedagogy, and content knowledge (TPACK). The The program was found to have positive impacts to varying degrees on teachers’ development of TPACK. Contextual factors and teachers’ pedagogical reasoning affected teachers’ ability to enact in their classrooms what they learned in the program. Suggestions for designing effective professional development programs to improve science teachers’ TPACK are discussed.