Estimates of developmental models of processes involving contextual influences (e.g., child care arrangements, divorce, parenting, neighborhood location, peers) are subject to bias if, as is often the case, the contexts are influenced by the actions of either the individuals being studied or their parents or teachers. We assessed the nature of the endogeneity biases that may result, discuss the importance of such biases in practice, and suggest possible ways of avoiding them. Our primary recommendation is that developmentalists consider reorienting their data collection strategies to take advantage of real or "natural" experiments that produce exogenous variation in family and contextual variables of interest.