We observed 32 subjects whose biological parents were both unskilled workers. Abandoned at birth, the subjects had been placed at approximately 4 months of age into families spanning the top 13% of the socio-professional scale. The effects of this change in social class were estimated by comparisons with groups of children of unskilled workers observed in two large scale studies. An internal control group was also available for 20 of the 32 subjects: the biological half-siblings who had been reared in their 'natural' environment. The effects observed are an increase of 14 IQ points in the mean IQ score estimated with 2 tests and a reduction by a factor of 4 in the probability of repeating a grade. These are significant despite the small number of subjects; we have shown that the bulk of these effects cannot be attributed to methodological biases. Our observations thus provide a direct quantitative answer to the question posed by Jensen in 1969. © 1982.
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