While testing this it will be handy to have two browsers, ie FF and chrome, so you can be logged in as admin and a student at the same time. As admin... Check that you have the system setting enablegroupmembersonly turned OFF. In a course create two groups. Then create two groupings. Put one group in each grouping. Give them all names that you won't get confused ie "first group" "first grouping" "second group" "second grouping" or similar. Put a student into one of the groups (remember which one). Edit an activity, show advanced and set "grouping" to the grouping the student is in. As student go to the user report for the appropriate course. You should be able to see the activity. As admin, set the activity grouping to the other grouping. As student refresh the user report. You should still be able to see the activity. As admin turn on enablegroupmembersonly. Go to the activity settings and check "Available for group members only" if it isnt already. As a student refresh the user report. You should now NOT be able to see the activity as its assigned to a grouping the student is not in. As admin edit the activity and set the activity to be for the student's grouping. As student refresh again and now you should be able to see the activity.