From an evolutionary perspective, the normal social play of children involves kids of various ages. Our human and great-ape ancestors most likely lived in small groups with low birth rates, which made play with others of nearly the same age rare. Consequently, the evolutionary functions of children's social play are best understood by examining…

Observation of 200 children ages 4 to 19 attending a Massachusetts nongraded alternative school disclosed substantial age mixing. Younger children used older children to develop skills and acquire knowledge. Age mixing encouraged opportunities for creativity, helped match abilities, and fostered older children's sense of responsibility for younger…