The revolutionary concept of free, nonsectarian public schools spread across America in the 19th century. By 1970, America had the world’s leading educational system, and until 1990 the gap between minority and white students, while clear, was narrowing. But educational gains in this country have plateaued since then, and the gap between white and minority students has proven stubbornly difficult to close, says Ronald Ferguson, adjunct lecturer in public policy at Harvard Kennedy School (HKS) and faculty director of Harvard’s Achievement Gap Initiative. That gap extends along class lines as well. By eighth grade, Harvard economist Roland G. Fryer Jr. noted last year, only 44 percent of American students are proficient in reading and math. The proficiency of African-American students, many of them in underperforming schools, is even lower. “The position of U.S. black students is truly alarming,” wrote Fryer, the Henry Lee Professor of Economics, who used the OECD rankings as a metaphor for minority standing educationally. “If they were to be considered a country, they would rank just below Mexico in last place.” Harvard Graduate School of Education (HGSE) Dean James E. Ryan, a former public interest lawyer, says geography has immense power in determining educational opportunity in America. As a scholar, he has studied how policies and the law affect learning, and how conditions are often vastly unequal. His book “Five Miles Away, A World Apart” (2010) is a case study of the disparity of opportunity in two Richmond, Va., schools, one grimly urban and the other richly suburban. Geography, he says, mirrors achievement levels.