A large empirical literature documents a rise in wage inequality in the American economy. It is silent on whether the increase in inequality is due to greater heterogeneity in the components of earnings that are predictable by agents or whether it is due to greater uncertainty faced by agents....

This paper develops a model of skill formation that explains a variety of findings established in the child development and child intervention literatures. At its core is a technology that is stage-specific and that features self productivity, dynamic complementarity and skill multipliers....