I have found as I have worked with online evaluation that a rubric template is very helpful for communication between student and instructor. There is so much information shared with online assignments and discussions that a systematic focus on what is the perception of the teacher for evaluation purposes should be made. Jennifer Wojcik, Chair for the Performing Arts, at the Gunnery School in, Washington, Connecticut, a colleague, and a super facilitator for Boston University, developed the format for the below document and it is very helpful. It provides guidelines for evaluation and for each course that I have taught I have modified it.
Discussion Rubric Template
Synchronous Conversation Interaction Evaluation