Having a lot of students that are happy and healthy isn't enough, eventually a school is for education. Without any teachers your students won't learn a thing. You also need to take care of your teachers. Keep them happy and healthy and make sure they do not have too many students  in the same classroom. Control their loan and train them to give them some more experience. The better your teachers are, the higher the grade of your students. Take control and become a great headmaster.