Today, Bernie Sanders visits Philadelphia, the biggest city in a state critical to his insurgent bid’s narrow path to victory. Before taking the stage and delivering his stump speech, he should know that there is no more salient social justice issue in this city than public education: Public schools have been gutted by deep Republican cuts, the rapid spread of expensive-to-fund and barely-regulated charter schools, and mass school closings. Though Americans have roughly 50.1 million children in public schools, neither candidate has spent much time discussing K-12 education.