Most of the research on argumentation in science education has documented the myriad flaws in students' argumentation, and the difficulties teachers have organising productive arguments in the classroom. We apply a sociocultural framework to argue that productive argumentation emerges from a classroom culture in which its practice meaningfully serves classroom goals. We present a case study using interaction analysis to contrast two elementary teachers' efforts to organise productive scientific argumentation in their classrooms. One teacher used discourse moves to orient students to each other's contributions in ways the other did not, reflecting differences in underlying aims for collective versus individual sense-making. This analysis shows that connecting discourse practices specifically to a goal of collective sense-making promotes productive argumentation.