Helen Epstein, in an aside in her fine piece on public-health innovator Sara Josephine Baker, suggests it rises partly from the excellent healthcare, daycare, and social services we give our military:
[T]here is one group of Americans that receives high-quality government-subsidized child-care services, including day care, preschool, home-visiting programs, and health care: the US military. Unlike the Soviet version, these comprehensive programs aren’t designed to create obedient little soldiers. Instead, they use a play-oriented approach to help bring out children’s individual cognitive and social capacity. This may help explain why military children score higher on reading and mathematics tests than public school children, and why the black/white achievement gap is much lower in military families than it is in the general population. Since the military child-care program was created in 1989, the government has repeatedly declined requests to fund an in-depth evaluation, perhaps because if the effects were known, all Americans would demand these programs for their children too.
via The Doctor Who Made a Revolution by Helen Epstein | The New York Review of Books.