Most of America’s major cities have made little to no progress reducing racial segregation in their public schools over recent decades. Many have slid backward, and are more polarized today than they were at the turn of the century. These challenges were highlighted in Nikole Hannah-Jones’s wrenching New York Times Magazine piece in September about her experience sending her daughter to poor, intensely segregated public schools in New York City as part of a campaign to fix them — only for her child to fall behind in her education and demand a change to a more selective school with fe...