Dick Lane made this suggestion in another thread. I would like to second his recommendation that in the grades area of WW, students be given a number (or percent) such as Total Correct out of Total Problems. So a running total that also reports as a percent.
This percentage is what I typically use for course grade computations. Also, I think students resonate with percentages. If a student sees a percent like 55%, they will recognize that as an F. My hope is that this kind of feedback could encourage them to work harder.