The capacity to reason critically and negotiate ideas and differences lies at the heart of quality education. Through critical reasoning we construct, organise, and justify knowledge; and we create new ideas and practices. Despite the emphasis on teaching argumentative writing in school curricula, existing research consistently shows that arguing well presents significant challenges to students of all ages and backgrounds. This paper argues that addressing this issue requires a novel understanding of argumentation not being so much a written form but a form of critical reasoning--the ability to reason, critique justify and evidence. Using classroom video recordings of two primary literacy classes and interviews with the teacher, and drawing on the pedagogic register analysis, the paper identifies pedagogic practices that support the development of students' abilities to take a stance, inquire about attitude, and reason with evidence. The findings have important implications for the design of effective pedagogic practices to expand students' potential to reason and critique across primary years of schooling.