his paper presents formal models of child development that capture the essence of recent findings from the empirical literature on child development. The goal is to provide theoretical frameworks for interpreting the evidence from a vast empirical literature, for guiding the next generation of empirical studies and for formulating policy. We start from the premise that skill formation is a life-cycle process. It starts in the womb and goes on throughout most of the adult life. Families and firms have a role in this process that is at least as important as the role of schools. There are multiple skills and multiple abilities that are important for adult success. Abilities are both inherited and created, and the traditional debate of nature versus nurture is outdated and scientifically obsolete. The technology of skill formation has two additional important characteristics. The first one is that IQ and behavior are more plastic at early ages than at later ages. Furthermore, behavior is much more malleable than IQ as individuals age. The second is that human capital investments are complementary over time. Early investments increase the productivity of later investments. Early investments are not productive if they are not followed up by later investments. The returns to investing early in the life cycle are high. Remediation of inadequate early investments is difficult and very costly
