The issue of how the external world becomes part of the behavioral repertoire of children has been important to psychology from its very beginning, preoccupying theorists from Sigmund Freud to George Herbert Mead. But ever since Lev Vygotsky claimed that every function in a child's activity appears first as a process in the social realm between individuals and moves to a process that individual children can accomplish relatively independently, there has been increased debate as to exactly how th...