Philadelphia’s Curtis Institute may be the most exclusive music school in the world. “Curtis has thrived under the smiling and benevolent leadership of Gary Graffman, who, himself a Curtis graduate (he entered the school at age 7) and major-career pianist, restored order to a turbulent institution after he took over in 1986. Now, Graffman has announced his intention to step down, and despite his strong leadership, the school will soon have to undertake enormous change if it wants to protect its much-envied traditions.”