This study investigated the characteristics of peer discussions used to support formative assessment in lectures, facilitated by a student response system, in an undergraduate qualitative methods course for psychology students. The intent was to examine the characteristics of peer discussions in which student response systems are used to facilitate the practice of formative assessment lectures. The research was guided by the following research questions: (1) What patterns of talk can be identified in the discussions? (2) How do the students use subject-specific vocabulary in the discussions? (3) How the students' understanding of the subject matter displayed in these discussions? To examine the characteristics of peer interactions, 87 student discussions were recorded and analysed. The concept of "exploratory talk" was used as a lens to examine the discussions. In 68 of the 87 discussions, the students exchanged ideas and elaborated on their peers' ideas and understanding of the concepts. In the remaining 25 discussions, the process of reasoning was less visible. The findings are relevant for teaching designs that aims to use digital tools to facilitate formative assessment.