[zie]

School districts spend most of their money on humans.

There is a LOT of infrastructure. The schools have to be built, they have to be staffed(there is a fair bit of support staff, to keep the teachers in classrooms teaching).

From cafeteria workers and janitors to IT people and payroll, back office and grant people. High Schools might have a few thousand students that congregate there every single day, that's a small town. Our local high school's have a dedicated full-time HVAC person for instance, just to keep the insane temperatures outside from getting into the classrooms.