Well, JForum's security schema works a bit different of that. Basically, there is not inheritance / level of permissions - all is based on the group's permissions.
As I said in the previous message, you can get close to it but only for "forum level", not "thread level". I mean, you can have a Teachers group that is allowed to write and read on any forum, and a Student group that is allowed to write and read the "Students Forum" forum, to only read the "Veterans Forum" and is not allowed to even see the "School Internal Discussions" forum.
That's all you can do with current JForum security schema (of course there is a bit more, as you can see in the Permissions page).
Rafael [originally posted on jforum.net by Rafael Steil]
Those are the largest trousers in the world! Especially when next to this ad: