This paper reports on a study concerning the social nature of young students' informal inferential reasoning. Employing inferentialism as a background theory, we examine cognitive and sociocultural aspects of reasoning that arose during group discussions as well as trace relations between those aspects. Following a design experiment approach, we analyzed the discussion that emerged while a group of second-grade students was working on a carefully constructed inferential task. The results illustrate the dynamic interplay between cognitive and sociocultural aspects of informal inferential reasoning during students' attempts to reach a conclusion while working in a group.