A structural-behavioral model of development is described as providing a basis for formulating hypotheses about the effects of biological risk factors on the development of children. It takes into account the contributions to development that come from organismic and environmental variables. These influences are modified by the effect of individual resiliency in the face of social and biological risk factors. Organismic, environmental, and individual differences are seen as making different contributions in different domains and at different periods of development. A distinction is made between the development of universal and nonuniversal behaviors. From this model, hypotheses can be derived about the effects of social and biological risk factors. The implications for developmental research designs are disccussed as are the kinds of behavioral measures most likely to be sensitive enough to detect the effects of social and biological risk facors on the development of children.