Elliott recalls the effect of this “lesson” on the way students behaved: “It was just horrifying how quickly they became what I told them they were.” Within half an hour, Elliott continued, a blue-eyed girl named Carol had changed from a “brilliant, carefree, excited little girl to a frightened, timid, uncertain, almost-person.” Not surprisingly, in the hours that followed, the brown-eyed students came to life, speaking up more and performing better than they had before. The prophecy had been fulfilled: Because the brown-eyed children thought they were superior, they became superior in their classroom performance; they also became “arrogant, ugly, and domineering” toward the blue-eyed children. For their part, the blue-eyed children began underperforming, becoming the inferior people they believed themselves to be.

Schooling molds a diverse population into one society sharing norms and values. This is one reason that states enacted mandatory education laws a century ago at a time when immigration was very high. In light of the ethnic diversity of many urban areas today, schooling continues to serve this purpose.

A less common pattern is matrilineal descent, a system tracing kinship through women. Matrilineal descent, in which mothers pass property to their daughters, is found more frequently in horticultural societies where women are the main food producers.

How closely related do people have to be to consider themselves a “family”? In preindustrial societies, people commonly recognize the extended family, a family composed of parents and children as well as other kin.