General help

I have a course with very large numbers (30,000) run across multiple schools (300 approx).  I have set each school up as a group in the course and I will have up to 200 students per group along with approx 3 teachers.  I have restricted the teachers to access information, grade etc. on their own students only, but I would also like them to be able to create their own groups within their school.  My problem is that when I allow teachers make groups they then have access to the full list of students when I would like them to only be able to pull from their own group.  Is this possible or is there a better way to mange this?