Users can be teachers and a student in a course, so where you have a student that needs to be a teacher in a course and they are already a student in Codio (either in the same or different course), you can send them an invitation to the course and when clicked by the student they will be added as a teacher to that course.
If you wish these teachers to be restricted to only viewing the course but not to be able to add/edit/change the course content, you can do so enabling the Read Only switch. With this enabled, these teachers will not be able to switch into Edit mode or be able to access the course Admin area
