When self sign-up is enabled for a group, instructors are unable to prevent students from switching groups. However, as an instructor, you can turn off the self sign-up at any time. By turning off the self sign-up, you prevent students from switching groups.
In Course Navigation, click the People link.
Open Group Set
Click the View User Groups button  or an existing group set .
Click the Group Set Settings icon , then click the Edit link .
Turn Off Self Sign-up
Make sure that there is not a check mark in the Allow self sign-up checkbox to turn off the self sign-up . Click the Save button .
Disabling self sign-up prevents students from moving between groups on their own. You will need to move them between groups and sign the students up for groups as needed.