A friend of mine used to work in IT at a school district where the dropout rate was high and the students' performance was terrible. Money poured into the school and was spent like water. Nothing changed. Why?
Studying or staying in school is a personal decision, it is not a collective one. If a student and their parents don't care about school, then all the money in the world isn't going to change anything. If you're the kind of parent who doesn't go to report card night and talk to the teachers, the school could have a helipad and an astronomy observatory and you still wouldn't go. If you're a student and you smoke weed at lunch in the parking lot, the school could have holograph-generating computers teaching chemistry and you'd still be getting high with your stoner friends.
What the chart above shows is that we passed the point at which investment affects performance long, long ago. Everything added on from here on out is just a waste of money.
Chart used without permission from an article on school choice from the Heritage Foundation.