This is what I use (points are just an estimate... please change for each course)
Excellent (26-30 points)
The student posts response to discussion on time and includes all the components required to answer the question.
The student interacts with other students, providing constructive feedback, new perspectives and asking thought provoking questions. All interactions are courteous and well written.
The student demonstrates an in depth understanding of the subject matter and supports ideas with examples from the reading or from related personal experiences.
Sufficient (21-25 points)
The student posts response on time and includes most of the components required to answer the question.
The student interacts with other students and provides feedback. All interactions are courteous and well written.
The student demonstrates an in-depth understanding of the subject matter.
Minimal (1-20 points)
The student posts response on time but does not respond to the elements required to answer the question.
The posted responses do not enhance discussion or provide good feedback to other students.
The student demonstrates minimal understanding of the subject matter.