Not sure you can blame administrative overhead. An assistant principal was telling my wife yesterday that administrators have to work much harder than teachers.
I blame the way our society has gone to put all these burdens on schools. Desegregation, enforced lack of being able to discipline are a huge part of the problem. A society more concerned about where a student can go to the bathroom than if the students are learning. Administrators have to handle all these burdens that should not be there.