Using topic or forum restrictions, you can create discussion areas where members of a group or section can collaborate on assignments or discuss course material in small teams. You can also use restrictions to create separate forums or topics for each group or section in a course offering.
Note: The disadvantage of using these steps is that a separate topic and grade item would need to be created for each group.
To open the forum or topic to everyone again, clear the Restrict this <forum/topic> to the following groups and sections check box.