Theoretical predictions, based on the confluence model, were made for data from six national surveys of intellectual performance. All six surveys relate intellectual performance scores to family configuration variables. Widely divergent patterns of relationships between the major family factors, such as birth order and family size, and intellectual performance scores characterize the six data sets. Nevertheless, the confluence model was capable of accurate prediction in all cases when all three parameters were estimated. Little accuracy was lost using only two parameters. Variations in the estimated parameter values that reflected the variations in patterns of effects could be meaningfully interpreted for their psychological significance.The effects of family configuration variables, such as family size, birth order, and spacing between siblings, on intellectual growth were recently described by means of the confluence model (Zajonc & Markus, 1975). A reparametrization of this model was subsequently employed to explicate the conflicting results reported in the birth order literature (Zajonc, Markus, & Markus, 1979). This paper reports more stringent and extensive tests of the confluence model than have been carried out thus far. A variety of data sets on the relationship between family configuration variables, such as birth order and family size on the one hand, and intellectual performance scores on the other, have been compiled and the parameters of the model were estimated for these data. These data sets, which come from large national intelligence surveys, show markedly divergent patterns of results. Thus, for example, in one data