Scientific argumentation can provide students and teachers with opportunities to use evidence to make sense of the phenomena being studied and to engage in central practices of the scientific community. We posit that fostering the practice of argumentation requires transforming classroom interactions in order to create a need for students to attend to each other's claims and evidence. This paper examines the enactment of a 7th grade ecology unit created to generate this need and support these discussions. Our analyses of the student discussions show students moving beyond typical classroom interactions in order to understand the ways in which their claims differ and to evaluate one another's claims, in light of the evidence. Thus, we conclude that this approach of creating a need and supporting students as they attend to and critically evaluate one another's claims and evidence appears to be a promising strategy for fostering scientific argumentation.