Let's understand Skodak and Skeels, finally1

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Abstract
The well‐known study by Skodak and Skeels (1949), in which one hundred infants who were born to unwed mothers of below‐average IQ and were adopted into superior foster homes and grew up to obtain Stanford‐Binet IQs averaging 20 points higher than the IQs of their biological mothers, has frequently been interpreted as a contradiction of the evidence for the high heritability of intelligence. It is here shown that this is a misinterpretation of the Skodak and Skeels results, based on failure to consider the prediction made from a simple polygenic model of parent‐offspring resemblance. The Skodak and Skeels data, when analyzed properly in terms of a quantitative‐genetic model, are found to be not all improbable or contradictory of a broad heritability for IQ in the range of .70 to .80. Also, the common fallacy of generalizing the results of Skodak and Skeels as an environmental explanation of the cause of the approximately 1 σ mean white‐Negro IQ difference is explicated from the standpoint of genetic theory.