My teachers are receiving a message to "contact the Administrator" for a password

This message would come up if you import a password for your teachers. For these teachers, let them know what password you imported. 

Alternatively, you can reset the password for all your teachers. To do so, go to the Global Setup / Contacts Setup page, Advanced Options, Default Password section. Optionally, you could change the default password setting. Then select the Reset Admin Passwords button to reset all passwords for your teachers.