There are many ways of engaging students in the material, some more effective than others. Students have their own preferences for information acquisition and using several methods helps reinforce the material. My experience is that asyncronous discussions are more effective than synchronous as it gives people a chance to really think about their response. "Read and respond to at least two other learners with substantive responses" is extremely effective to reinforce material, especially if you don't agree; professional disagreement and discussion follows.
