This discussion aims to get students to agree on a single answer. For this to occur, students must work together and determine what points on which they can agree. They don't have to get the correct answer, but one that has agreement from the group. This kind of discussion should focus on compromise and identifying similarities and differences. It can be tricky and requires students to understand a process for reaching a consensus. It would be best if you outlined this for students as there are distinct phases:

Introduce and Clarify - students seek to understand the problem at hand and ask questions about the definitions and parameters of the problem.
Explore Ideas - Open the discussion as an exploration to seek common and shared understanding.
Form a Proposal - Work towards a position and a shared group statement. It doesn't have to be finished or perfect, but a start.
Test the Proposal - Test the position and see how it performs for the group. Does it address the problem?
Amend the Proposal - Iterate between testing and amending the statement until there is no more movement.
Submit the Proposal - Circulate the final statement from the group.