One of the hallmarks of science and science education is the production of new knowledge about the natural world through objective argument and critique. Teachers' understanding of scientific argumentation impacts how they incorporate this important scientific practice into science classrooms. This study examined how three professional development workshop series grounded in authentic practice impacted 70 elementary, middle, and high school teachers' pedagogical content knowledge (PCK) for scientific argumentation. Data sources included pre- and postsurveys, videotapes of the workshops, artifacts produced by the teachers, and samples of student writing. Results from the analysis suggest that the workshops were successful in teachers' development of PCK for argumentation in relation to the structural components of students' science writing. However, the teachers also had a number of challenges. Specifically, teachers struggled with analyzing classroom discussions for both structural and dialogic characteristics of argumentation, had difficulty applying the reasoning component of argumentation to classroom practice, and found designing argumentation questions to be challenging. Finally, elementary teachers connected argumentation to other disciplines whereas high school teachers focused more on the science content. These challenges and differences between teachers should be considered in the design of future professional development and preservice teacher education.