In dozens of U.S. cities, more than one in five students now attend charter schools. Charter school expansion has fueled an increasingly energetic discussion among advocates: How large a share of urban schools should be charters? Is the ideal New Orleans, where nearly all public schools are charter schools? Or does that create demands on charters…

Since the run-up to the 2008 election, the Democratic Party has been home to two prominent and very different reform wings. One, spearheaded by the group Democrats for Education Reform and notable school-district chiefs like New York's Joel Klein and Washington, D.C.'s Michelle Rhee, is the Education Equality Project (EEP). The other, A Broader,…