In recent decades, research has stressed the prominence of mathematics classroom discussions in productive instructional practices in mathematics instruction. In this context, problem-solving activities have been a common focus of research. Research shows that teachers need to deal with prerequisites and challenges such as norms, design of tasks, activating students, and leading students' discussion to achieve a productive whole-class discussion. However, another promising activity for achieving productive discussions involves using a classroom response system and implementing different task types in a multiple-choice format. There is little knowledge about whole-class discussions using this approach. To meet this need, this paper presents results from a mixed-method approach that characterizes whole-class discussions to explore the potential of multiple-choice tasks supported by a classroom response system to achieve productive whole-class discussions. Three types of multiple-choice tasks were implemented in the classrooms of twelve mathematics teachers at secondary schools. The lessons, including 35 whole-class discussions, were video-recorded, transcribed, and analyzed. The results summarize the characteristics of these whole-class discussions, including measures of students' opportunities to talk and teacher and student actions. These results can help us develop a more profound understanding of whether and how multiple-choice tasks supported by a classroom response system can support teachers in achieving productive whole-class discussions.