Need to create a school wordpress multisite

Hi,

I need some ideas on using wpmu plugins for my set up.

1. A school has 20 teachers and 100 students.
2. Each teacher can teach all students.
3. Only teachers have sites eg. teacher1.xxx.com, teacher2.xxx.com.
4. How to allow each student to access all the sites?
5. How to group students to different class eg. Class1a,Class 1b

Please advise