There is this fantasy that going to a privately managed school would lead to higher test scores, and higher test scores would lead to the end of poverty. All of that would be just great—except none of it is true. I mean, it’s a fact that every test that’s given anywhere in the world shows that family income is a decisive factor: the kids who come from affluent families are at the top, and the kids who come from poverty are at the bottom. That’s simply a fact; it’s not an opinion. It’s true on international tests, it’s true on state tests. You name the test—the ACT, the SAT—poverty is decisive.
Back to School, Nika Knight interviews Diane Ravitch - Guernica / A Magazine of Art & Politics (via guernicamag)

But not as a direct cause af the low grades. If the child’s family is poor he ir she probably has to work, ergo he or she can’t be 100% committed to school.