Moodle allows you to divide your students into groups. You can then use the groups to divide activities. For example, if you use groups with a forum each group would get a different copy of the same forum. You can set the forum to prevent or allow students in one group to see postings done by members of another group.
See the group documentation at Moodle.org for a discussion of the types of groups. You must adjust the course settings to all for groups before you can create any.