Aim for class sizes of say 350 - 550. Have a set number of administrators tied to class enrollment numbers. It should be relatively easy to create a standardized matrix based on number of students.

You need 1 counselor per X students and once a you reach 110% of that work load, you hire another counselor. Rinse and repeat for deans/vice principals, etc.

Do the same thing in reverse for schools that are losing enrollment. Once you fall below Y level, you are absorbed into the next closest school and the affected teachers can have priority for applying for openings over "green" employees.