Personas for any user depend on roles and tasks the user has.
All users in the system have the All School role. If a user has only the Teacher role (aside from All School), they will not see any additional Personas (such as onCampus), and will work under a Faculty persona.
If your Teachers have additional responsibilities and roles (ex. if you have a Teacher that is also an Academic Group Manager, and Attendance Manager), they will see their Faculty persona, as well as onCampus and onRecord.
If you have questions regarding why a teacher (or other user) is able to access other personas or has too much access - or, if you need assistance adding access for a user, please contact Support with specific details for the user and changes you would like to make.