One focus of 21st century science education is teaching students authentic disciplinary practices. Scientific argumentation is one such practice, and evidence suggests it is not only a key skill, but also a facilitator of high-level comprehension. Science teachers need assistance teaching and incorporating argumentation into their work. In this study, we implemented Quality Talk, a small-group discourse model shown to foster argumentation and conceptual understanding, in four high school science classrooms. Using a quasi-experimental design, we found Quality Talk students, compared to control group students, displayed better verbal and written argumentation. Conceptual understanding performance did not differ by group, but post hoc analyses suggested new directions for improving Quality Talk and other methods of fostering scientific argumentation and understanding.