Jen,
Yes - you would create a root group for each of the classes (9th, 10th, 11th, 12th graders) and under the group - you would create a role for each of the parents that defines that they have access to and apply it to the user.
You do not need CB at all for this type of setup. the software does however work with CB - it only syncs with the CB tables - so there is no work on your end other then installation of a plugin if the installer does not install it for you.
I do not see any red flags as of this moment.
Kindest regards,