I would like to set up a forum in a course that contains many (potentially hundreds) of groups. The forum would consist of a fixed number discussion topics, which the students enrolled in the course would reply to. I'd like the students to only be able to see replies from other students in their group. I'm able to create this scenario by setting the course and forum activity group modes to separate, then creating duplicate discussion topics for each group. The problem is that the number of groups multiplied by the number of discussions per group equals a prohibitive amount of setup time. I'd like to find a way to set this up without needing to specify the group at the discussion topic level. I've tried adding the discussion topics and setting the group for each to "all participants". This seems to get most of the way there, but the discussion topics can't be replied to by students.
Can anyone suggest another way to go about this? Other configurations or perhaps a different activity type?