There are a variety of ways to assess discussions in an online course. Rubrics provide a concrete and descriptive summary for the learners. Students find rubrics helpful, especially if they are new to learning online.
You may choose to use or adapt rubrics for your own course.
Here are some other sample rubrics found on the web. If you choose to use one of these, you may need to get permission from the author first. To find others, search on: online participation rubric.
Discussion Rubrics Many good examples here.
Aimee DeNoyelles, Amy Sugar, Kelvin Thompson, Jessica Vargas and Baiyun Chen (2011). Discussion Rubrics. In K. Thompson and B. Chen (Eds.), Teaching Online Pedagogical Repository. Orlando, FL: University of Central Florida Center for Distributed Learning. Retrieved October 19, 2012 from http://topr.online.ucf.edu/index.php?title=Discussion_Rubrics&oldid=2197