Students who have dropped your course are not automatically removed. If you need to drop a student yourself, please do NOT delete them from WebWork. Instead, do the following.
We don't want you to delete students because once you do, all of their data is lost. Students sometimes drop a course and then re-add, either by choice or, e.g., for not paying student fees. We don't want their data deleted in case they need it again. You can always go back and change their status from “Drop” to “Enrolled” if necessary.