OK - go to site administration>front page>front page settings and scroll down and make sure the default front page role is set to "none"
Then go to > users>permissions>assign system roles and make sure you have NO students assigned the role of student in there - they should only be students within their course
Then go to >users>permissions>user policies and check your default role for all users is "authenticated user"
That should do it - if not, come back