Ok, that worked. I was able to add an access level called Class Access and granted that level of access to a group called Class Member. Then in Bible Study I was able to restrict access to the Class Member group.
It would be very helpful to have the same option for a Series. This would avoid needing to set the access level for each study, but simply set it for the series (which in our case would be the class or course of lectures).
Thanks for the app! It's looking like it will work out great for us.