In his campaign for Mayor of New York City, Bill de Blasio positioned himself as the candidate most determined to break with the legacy of the outgoing Michael Bloomberg administration. Voters responded enthusiastically, handing de Blasio a nearly 50-point margin of victory in the November 2013 election. De Blasio, a Democrat, interpreted the win…

Data-driven instruction began its spread across the country about a decade ago, in the footsteps of the No Child Left Behind requirement that schools administer yearly achievement tests. Those tests didn't help teachers spot and backfill learning gaps, though. Scores came back after everyone had moved on to the next grade, and anyway, the tests…