We develop a Roy model of social interactions in which individuals sort into peer groups based on comparative advantage. Two key results emerge: First, when comparative advantage is the guiding principle of peer group organization, the effect of moving a student into an environment with higher-achieving peers depends on where in the ability…

Troop ideology as defined by the scoutmaster and other involved adults radically altered the learning experiences of boys in two Boy Scout troops, even though both adhered to the official program. Using observation and interviews, researchers studied all aspects of the troops over 7 months. One troop, whose scoutmaster was benevolent and…