This paper formulates and estimates multistage production functions for child cognitive and noncognitive skills. Output is determined by parental environments and investments at different stages of childhood. We estimate the elasticity of substitution between investments in one period and stocks of skills in that period to assess the benefits of early investment in children compared to later remediation. We establish nonparametric identification of a general class of nonlinear factor models. A by-product of our approach is a framework for evaluating childhood interventions that does not rely on arbitrarily scaled test scores as outputs and recognizes the differential effects of skills in different tasks. Using the estimated technology, we determine optimal targeting of interventions to children with different parental and personal birth endowments. Substitutability decreases in later stages of the life cycle for the production of cognitive skills. It increases in later stages of the life cycle for the production of noncognitive skills. This finding has important implications for the design 10 To focus on the main contribution of this paper, we focus on investment in children. Thus we assume that θ T+1 is the adult stock of skills for the rest of life contrary to the evidence reported in Borghans, Duckworth, Heckman, and ter Weel (2008). The technology could be extended to accommodate adult investment as in Ben-Porath (1967) or its generalization (Heckman, Lochner, and Taber, 1998). 12 This formulation assumes that measurements a ∈ {1, 2, 3} proxy only one factor. Carneiro, Hansen, and Heckman (2003) consider alternative specifications, but in a much less general econometric model. The key idea in all factor approaches is one normalization of the factor loading for each factor in one measurement to set the scale of the factor and some measurements for each measurement of type a dedicated to each factor. It is clear that even within the framework of this paper, as long as some of each of the measurements of type a satisfy the assumptions in this paper, one can identify the factor loadings of the remaining measurements that do not satisfy the assumptions if, for example, the factors are mutually independent. 22 See the Web Appendix for a more detailed derivation of the likelihood function and filtering equations (see Web Appendix Section 3 and Web Appendix Section 6.4). Section 6.4 presents the full model with heterogeneity and investment equations.