You can create a message that goes only to the teachers of a student (or multiple students).
To do that, you would only have the Teachers Icon selected as shown below:
When only Teachers icon is selected, the message will NOT go to the student/guardian, but just the teachers. Their reply will also only go to the included teachers.
You will then see the message with the Teacher Only as shown below:
At any point in a shared message thread, you also can reply to just the teachers, by selecting that option in the pull down:
