In 1969, Mark Edmundson was a typical high school senior in working-class Medford, Massachusetts. He loved football, disdained schoolwork, and seemed headed for a factory job in his hometown--until a maverick philosophy teacher turned his life around. When Frank Lears, a small, nervous man wearing a moth-eaten suit, arrived at Medford fresh from Harvard University, his students pegged him as an easy target. Lears was unfazed by their spitballs and...