[N]o Child Left Behind had at least one significant -- and, experts say, lasting -- success: It changed the way the American educational system collects and uses data. The law may not have achieved the promise of its title, but it did force schools across the country to figure out which students were being left behind, and to make that information public. Education experts argue that the law's true legacy is the way it laid bare the inequities in the American educational system, and forced districts, in some cases for the first time, to address them.

"There's a very long history of states and school districts and schools essentially hiding behind the average performance of their students," said Scott Sargrad, a former Education Department official in the Obama administration who is now a researcher at the left-leaning Center for American Progress. "That masks really significant differences between kids who are more affluent, who are white, who don't have disabilities, whatever it is, and their peers who are more disadvantaged."

In some districts, merely drawing attention to racial or other disparities was enough to drive real changes. No longer able to coast on the strength of their high-performing majority, districts such as Beverly adopted new programs aimed at identifying and helping struggling students who might otherwise have fallen through the cracks.