Online learning in an academic setting requires a great deal of focus on discussion posts. When the face2face element is removed, student-student and student-faculty engagement generally occurs on the discussion boards. This put the discussion board at the center of student learning, and many studies have demonstrated how effective gently-guided discussion can be in achieving deep learning. It is therefore crucial to establish from the get-go a set of expectations on how posts will be graded. This is where rubrics can be very handy. A rubric not only defines your specific expectation as far as what makes an exemplary post, but it also acts as a mechanism to support your grading later on should a student receive a less-than-expected grade. Rubrics not only help students to understand how best to prepare an assignment, but also ensure grading is more objective and fair in both the eyes of the student and the instructor.
Here is an example of a discussion board rubric I use in an online graduate class: