A summary and discussion of a series of studies considered the dilemma that equal educational treatment of all children in public schools appears likely to increase the spread of differences among them in educational achievement. Longitudinal studies of pairs of identical and of fraternal twins in Sweden from 10 to 18 years of age considered the similarity within pairs in height and in weight over a span of six years for girls and eight years for boys. Similar studies of correlations in test scores for verbal, mathematical, inductive reasoning, and perseveration abilities led to the conclusion that the achievement tests showed more environmental and less genetic influence than the aptitude tests. Studies of achievement test results in relation to socioeconomic levels showed a large decline from third to sixth grade in the correlation for fraternal twins in the lower socioeconomic group but not for identical twins and not for twins in the higher socioeconomic groups. The studies proposed mastery learning as a method for attaining equality of learning outcomes and concluded that genetic and environmental effects and their interactional and correlational effects can be manipulated by varying environmental permissiveness or restrictedness. (CTM)