Support for the confluence model of intellectual development has come from analyses of family size-birth order means of large aggregate data sets. Analyses of individual scores do not substantiate the confluence model, as explained variance is markedly reduced. The study of family interaction variables utilizing longitudinal data is recommended.…

Assessments of the home environments of 116 families whose twins were participants in a longitudinal study of early mental development were conducted. Predictions of offspring intelligence scores increased from ages six months to six years old. Although home/family variables were related to mental development, so were parental education and SES.…