“Assessment of Effects of Socio-Economic Status on IQ in a Full Cross-Fostering Study”, 1989-08-17 (; backlinks; similar):
An important question in studies of mental ability concerns the effect of parental socio-economic status (SES) on the IQ of their offspring. Only a full cross-fostering study, including children born to biological parents from the most highly contrasting SES and adopted by parents with equally contrasting SES, can answer this question.
Previous adoption studies using incomplete cross-fostering designs1–3 have indicated an effect of postnatal environment on the IQ of children born to low-SES backgrounds and adopted by high-SES parents. They have not shown whether a low SES reduces the IQ of children born to high-SES parents or whether the SES of biological parents has an effect on IQ, or whether the effect of the SES of adoptive parents is independent of the SES of biological parents.
We present a full cross-fostering study dealing with IQ, and find that children adopted by high-SES parents score higher than children adopted by low-SES parents; children born to high-SES parents score higher than children born to low-SES parents; and that there is no evidence for an interaction between these 2 factors on children’s IQ.