I have searched the forums for an answer and I have done everything I can to fix this problem. Please help!
As it stands, all of my students will be able to see all of my courses and post assignments in each, even if I haven't added them as a "student" within the course.
I have also made these changes.
Admin>users>permissions>assign system roles
Only admins and course creators are added
Admin>front page>front page roles
Only admin and teachers are listed
I have 2 course categories:
6th Grade & 7th Grade
Each of these categories have a Language Arts, Math, Science, and Social Studies course under it.
I want only 6th graders to be able to access 6th grade courses and vice versa.
Please advise.
I need to clarify my original statement: Guests can see the courses but cannot gain access to the courses.
Hi there. Go to site administration>users>permissions>user policies and make sure your default role is Authenticated user and NOT student.
If that doesn't make a difference, post back and I will suggest some other ideas
(Additionally, you don't need admin to have a front page role - they can do everything anyway. And unless you want all your teachers to be able to edit your front page I wouldn't advise giving them a front page role either.)
If that doesn't make a difference, post back and I will suggest some other ideas
(Additionally, you don't need admin to have a front page role - they can do everything anyway. And unless you want all your teachers to be able to edit your front page I wouldn't advise giving them a front page role either.)
Well. That was the fix for my problem and I appreciate your suggestions about the front page as well. I am changing that too. 
Help...please! My users (all roles) are in all my courses. How can I assign users to specific courses.
Denice,
If you have assigned roles on the front page, then that role will be for all the courses. It is always a good thing to go inside a course and then, assign roles to that course in specific.
If you have assigned roles on the front page, then that role will be for all the courses. It is always a good thing to go inside a course and then, assign roles to that course in specific.
I am having the same problem with my students being able to move around to all courses. The default role for all users was already set to authenticated Users. I changed the default setting in the course to Authenticated User, but that did not fix the issue.
What Moodle version?
looks like 1.9.8+
I've never seen Authenticated User as an option for a default setting in the course. Anyway, go to Course administration > Settings, and set the following parameters:
Enrolment plugins = Internal Enrolment
Default role = Student
Course enrollable = No
This way students won't be able to get into a course unless they have been specifically enrolled.
I think that in that scenario I would have to make the changes within each course. Ideally, I would like to be able to make a global change to all students that would not allow them to see the other courses, unless the teacher enrolled them. However I am beginning to think that that is not an option. Sorry, I am extremely new to using a Moodles, and thank you.