Create a couse. Enrol three non-editing teachers. Create two groups and put one non-editing teacher in each on. Put the third non-editing teacher in both groups. Put some students in both groups. Create an assignment. Set group mode to "Separate groups" Go to the course and then follow "Course administration ► Users  ► Permissions". Remove non-editing teachers from moodle/site:accessallgroups Log in as one of the non-editing teachers. Go to the assignment and the grading interface. In the student navigator "Top right hand corner" check that you only have access to students in your group (click the arrow to see a list of all of the participants). Press the left and right arrows and make sure that you only rotate through the members of the group. Log in as the non-editing teacher that is a member of two groups. Go to the assignment. On the first page there should be a group selector. Stick with the first group and click the "Grade" button. Make sure you only have access to the group selected on the previous screen. Go back to the first page and select the other group. Check that you now only have access to the members of that group. Log in as a normal (editing) teacher and check that you have access to all students in the grading interface. Regression testing. Now change the group settings to "Visible groups" and log in as one of the non-editing teachers. Make sure that you have access to all of the groups in the assignment grading interface. Now change the groups settings to "No groups" and log in as one of the non-editing teachers. Make sure that you have access to all of the groups in the assignment grading interface.