Swedish longitudinal studies of twins support Scarr-Salapatek's explanation of nature-nurture influences on intelligence. This model predicts more genetic variance in test results for advantaged than disadvantaged groups. Jensen's work, however, suggests equal amounts of variance among different social classes. (Author/CP)

As part of a continuing evaluation of the Swedish school system, changes in intelligence test scores from 1960 to 1995 were studied in relation to cohort, gender, and socioeconomic background. Changes in verbal, spatial, and reasoning ability were studied by comparing results on identical tests given to representative samples of Swedish…