First of all, these rights can be granted or restricted by administrative users to entire demographics or individual users in the Social Networking Manager tool. Barring that, its good to know that all teachers and all students from the same school can communicate. Teachers and students will not be able to communicate with teachers or students in schools to which they do not belong. Parents can only communicate and see messages from their own children and their children's teachers. Even in a thread with a large group, parents won't see any messages from children who aren't their own, nor will those children see theirs.