I've had the same trouble. After following a few examples found here, I'm still not sure how I can realistically set up a parent account in a straight-forward fashion.
In my case, i'd like parents to have access to a student's grades, view their courses and resources, but not be able to participate in activities
(in particular forums). At the same time, I would like to be able to set up a parent->teacher forum or some other online communication tool without student participation.
Roles are obviously very powerful, but i'm tending to believe that due to the nature of parents being linked to particular students, parent access almost needs to be developed into its own module. I imagine it's all possible with roles, but the navigational interface doesn't really exists.
Of course I could be missing something very simple, and I expect that once we understand the process for setting this up, the rest of these requests will fall into place.