Fleming, Debra. "Using Best Practices in Online Discussion and Assessment to Enhance Collaborative Learning." College Teaching Methods & Styles Journal 4.10 (2008): 21-40.
Explores online discussions in collaborative learning and methods for assessing student participation.
Vonderwell, Selma, Xin Liang, and Kay Alderman. "Asynchronous Discussions and Assessment in Online Learning." Journal of Research on Technology in Education 39.3 (2007): 309-28.
A case study examining asynchronous discussions in online graduate courses.
"Designing Online Discussions: Key Questions." Sheridan Center for Teaching and Learning.
Establishes a series of central questions for designing, responding to, and assessing online discussions.
"Generating and Facilitating Engaging and Effective Online Discussions."
Prepared by the creators of the Blackboard, a Learning Management System (LMS), but some of the practices described can be generalized to other environments as well.
Other pages that might be of interest: