How to do this?

Hi,
How can I achieve a setup like this with Groups? I’m doing a pro-bono project for a school and I am stuck with permissions.

class 1a parents )          )            )
class 1b parents ) All      )            )
class 2a parents ) parents  )logged-in   )content available
...              )          )users       )for logged-in
class 6b parents )          )            )& unauthenticated
                            )            )users
teachers                    )            )
                                         )
anonymous users                          )

I want it to based on category read control. Writing to other groups is fine and desirable.
Being able to control access to pages based on groups would be nice too.
I believe it is quite simple, but I would appreciate clear instructions very much.
I tried playing with press permit, but it’s so complex that I am afraid I’ve messed up my site and will have to reinstall.
Thank you in advance for any assistance.

http://ww.wp.xz.cn/plugins/groups/