So I have several family members who work in under privileged schools, and what they pretty unequivocally say to this argument is that it's one of those "it's expensive to be poor" kind of things.
These kid's parents work two or three jobs, so we give them subsidized after school programs. Their housholds are food insecure, so we give them breakfast and lunch so they can focus on schooling and not their empty stomachs.
So much of this spending is just to try and bring these students closer to parity in the moment, but despite all of that, they don't get any that before they enter school in kindergarten, so they're sort of perpetually behind. It has next to nothing to do with government waste, or throwing good money after bad despite what that terrible "Waiting for Superman" movie told all the white flight parents looking for validation.