Prevent activities specific to a group from being included in non-group members' gradebooks

Groups can almost be used to differentiate instruction in Moodle by setting up a course so that different groups can see only activities that are intended for them. The limiting factor is the students' gradebook. Hidden activities intended only for groups are still listed in the non-group members' gradebooks, and the corresponding activity points are still calculated in the non-group members' final grades.

It would be a great instructional advancement if students' gradebooks displayed and calculated only the activities available to them.