Argumentation is a central epistemic process contributing to the generation, evaluation, and application of scientific knowledge. A key challenge for science educators and researchers is to understand how the important social and discursive (“social dialogic”) dimensions of argumentation can be implemented in learning environments. This study investigates how science educators learned about such argumentation through a professional development program at a scientific research center. The 13-day program included 5-days working in research laboratories with a mentor and observing scientific argumentation in context. Theoretically, this research draws on sociocultural frameworks to investigate the social dialogic dimensions of scientific argumentation. Methodologically, it examines the reflections of a cohort of 21 secondary science teachers as they observed argumentation in scientific research settings. It examines how research experiences for teachers can promote an understanding of the social dialogic dimensions of argumentation and to help teachers take up educational approaches that foster expansive argumentation practices. Teachers shared a heightened awareness of argumentation as a ubiquitous, embedded feature of authentic scientific activity; expanded ideas about forms, uses, and purposes of argumentation; and developed an understanding of how contexts for argumentation such as collaborative sensemaking and critique can help manage uncertainty and build knowledge. A year after their program participation, teachers recounted shifts in pedagogical practices, including desettling traditional classroom talk patterns, scaling back their epistemic authority, providing students with more agency and ownership of ideas, and recognizing the value of establishing a culture of community and collaboration. Findings highlight how professional development in research settings has the potential to broaden teachers’ views of argumentation, with implications for secondary science teaching.