An admin can control which activities can be added to courses

1. Log in as a teacher, go to your course and click the 'Turn editing on' button.
2. Click the 'Add an activity or resource' link and check that you can add a chat and a glossary to the course.
3. Log in as an admin and go to Settings > Site administration > Users > Permissions > Define roles.
5. Edit the teacher role and remove the mod/chat:addinstance capability, then click the save changes button at the bottom of the page.
6. Go to the teacher's course and in Settings > Course administration > Users > Permissions, remove the teacher role for the capability mod/glossary:addinstance.
7. Log in as the teacher again, go to your course and click the 'Turn editing on' button.
8. Click the 'Add an activity or resource' link and check that you are no longer able to add a chat or a glossary to the course.