Ok so your teachers are teachers throughout your school and your students are students whichever class they are in. That doesn’t mean they have to be assigned those roles everywhere in Moodle. A common error, and an issue frequently raised in the Moodle forums is administrators seeing Site Admin>Users>Permissions>Assign System Roles and presuming this is how to enrol their students and staff. Aside from the fact that this puts everyone unneccessarily in all courses, even when they are not teaching them or studying in them, it runs the risk of giving unintended front page privileges to people. ( I once enrolled into a Moodle via email self authentication (see here) and found myself able to edit that Moodle’s front page….) So this post is a caveat really: there are cases where you might want teachers with site-wide rights, but for the most part, just use the course administration block in each course -this block  here.