This study aims to investigate whether structuring an interaction supports students' elaborative argumentation. The study compares the quality of secondary school students' (N = 16) argumentation during dyadic structured and unstructured computer-based chat interaction. The results suggest that structuring an interaction increases the proportion of argumentative discussion, whereas unstructured discussion seems to produce more elaborated argumentation. However, the results indicate that the discussion topic must be debatable in order to achieve critical and elaborative dialogue. Structuring an interaction can be used to foster counterargumentation on the topics that do not spontaneously provoke different viewpoints.