This step examines and refines the knowledge that was constructed in the reflective step, through discussion in the classroom. Viable knowledge is agreed in this way. In the constructive approach, four methodological issues should be devised. (1) The introductory problem as a rich source of children’s activities,(2) the five modes of representation, i.e. realistic representation, manipulative representation, illustrative representation, linguistic representation and symbolic representation, (3) the constructive interactions in which children make effort to attain some agreement based on their existing constructs, and (4) the reflective thinking, through which they abstract, generalize and logicize an essence of their actions and the outcome.