Dealing with scientific information on the Internet is an increasingly communicative activity. Two discourse features have been found to impact on the effectiveness of argumentative discourse activities: Critically questioning and elaborating on the partner's information. The present study investigated how these functional communication activities can be supported in argumentative discourses on scientific information. In a 1 × 2 between-subjects design, we established either a difference or a similarity focus by instructing dyads to pay attention to either differences or similarities in views and arguments while discussing the topic. Results showed that focusing on differences had beneficial effects on the quality of argumentative discourse as well as on individual critical thinking. However, on a socio-motivational level, participants' intrinsic motivation regarding the cooperation with the discourse partner and working on the tasks was higher when focusing on similarities. Implications for improving argumentative discourse and thereby fostering individuals’ critical thinking skills are discussed.