Theory of online education proposes three areas that must be present for successful education. The Social Presence, the Cognitive Presence and the Teaching Presence. The social presence is often encouraged by the use of discussion boards in a learning management system.
A standard practice is for students to write one post and then comment on a specified number of other student posts. Different rules pertain at different academies. Some institutions do not all responses until an initial post has been made. All of the rules are designed for assessment of discussion posts, rather than for encouraging a social presence. If social presence is the purpose of discussion board posts than the rules will have to change.
One idea that might improve the standard discussion board include breaking a large class into several smaller groups. My own experience with this is that unless all the discussion is done in the smaller group, most participants will do as little as possible in the small group. If the discussion emphasis is still with the bigger group, that’s where the energy will be directed. Students of all sorts are faced daily with cognitive load problems. Students of online classes have an increased load, merely due to the responsibility inherent in online learning. Unless your students are extrememly gregarious spreading the course effort into many different conversation puddles limits the effectiveness of all of them. One central discussion lake with a limited number of participants is preferred.