I think you need a bunch of background information to figure this out.
1. You need to how much power it takes to run the small school.
2. You need to know the wind patterns in that area and the average winds over a long period of time in order to determine the best location/height for the turbine.
3. You need to know which type of turbine is most efficient for converting those winds into kinetic movement (blade size or helical shape).
4. And you need to know the efficiency of the generator to be used.
It may not even be possible to run an entire school with the winds in that area.