Thank you for your post.
It sounds like you have everything set up fine. However, you may not want to do that with Notes. That is, you may have many notes per each student, but you won't have many students for each note. True? Therefore, it would be a one-to-many relationship. Therefore, each Note would have a staff_id (for the teacher writing the note) and a stu_id (associated with the student). Mostlikely, the teacher will be looking at a student record, and then want to attach a note.
In your Note table, you could select the teacher and the student before writing the note.
I'm not sure what the process is, but this may give you a couple of ideas.