Should I use django admin panel for regular users?
Yes you can use admin panel for your teachers. for this Purpose you need to mark them as staff to login in admin panel and set for them permissions you want to add them.
I am currently trying to make a learning app. The three main users would be the Admin, Teacher and Student. Should I use the django admin panel for the teachers ? It has  a lot of features and is fully customizable and I can choose what a teacher can do or not from there. Is this a correct approach ?