Does Higher Quality Early Child Care Promote Low-Income Children's Math and Reading Achievement in Middle Childhood?

Yes, says an article in Child Development.

Higher quality child care during infancy and early childhood (6–54 months of age) was examined as a moderator of associations between family economic status and children's (N = 1,364) math and reading achievement in middle childhood (4.5–11 years of age). Low income was less strongly predictive of underachievement for children who had been in higher quality care than for those who had not. Consistent with a cognitive advantage hypothesis, higher quality care appeared to promote achievement indirectly via early school readiness skills.

So it's partly that good child care helps ...

Family characteristics associated with selection into child care also appeared to promote the achievement of low-income children, but the moderating effect of higher quality care per se remained evident when controlling for selection using covariates and propensity scores.

And partly that people whose kids achieve more faster than their neighbors are the ones who put their kids in child care.