The ability for students to create discussions in groups is going to be controlled at the account level by your admins. It's a permission for the student role when it comes to creating discussions within a group page. The check box in your course settings only applies to discussions in the course, but technically the groups are separate.
Announcements are just a special type of discussion post. If you turn off the "Let students create discussion topics" in your course settings, that may take care of it.
The ability for students to create discussions in groups is going to be controlled at the account level by your admins. It's a permission for the student role when it comes to creating discussions within a group page. The check box in your course settings only applies to discussions in the course, but technically the groups are separate.
