user groups and roles/permissions

Does anyone have any suggestions/solutions for dealing with group permissions? A key use case we're trying to accommodate goes like this:

An instructor creates a blog for a class and would like to give all students in the class the Author role. Currently, they would have to collect all account names and manually assign the role to every user. We'd like to be able to establish groups of users, and then establish roles for those groups.

We implemented buddypress, since it has group functionality, hoping it might solve this problem. It doesn't seem that the BP groups have any real hooks into WP in this regard.

If there aren't any existing solutions, does anyone know if authorization checking code in WP is fairly well contained? If authorization is handled "centrally" then implementing groups shouldn't be TOO difficult. I'm guessing there is some fundamental blocking issue though, otherwise the feature would probably already exist.