Gary, I am not sure exactly what you are trying to do. Are you using Moodle's "group" features? Awhile ago, I had two sections of a course and I wanted to combine them into one Moodle course. However, I wanted to keep their discussion separate. I accomplished this by using groups. It was a little tricky to set up. I added another "me" user and had to modify the role a little, but it worked. Students in one group did not see posts from students in the other group.