THE PRIMARY PURPOSE OF THIS STUDY WAS TO TEST THE HYPOTHESIS OF DIFFERENTIAL HERITABILITY RATIOS FOR WHITE AND NEGRO CHILDREN ON TESTS OF SPATIAL ABILITY. IN A TABLE THE TWO GROUPS ARE COMPARED ON EIGHT SPATIAL ABILITY TESTS BY FOUR DIFFERENT HERITABILITY ESTIMATES. IT IS CLEAR FROM THE TABLE THAT ONLY THE OBJECT APERATURE TEST YIELDS CONSISTENTLY HIGHER HERITABILITY RATIOS FOR WHITE THAN FOR NEGRO CHILDREN. ON THE BASIS OF DATA PRESENTED IN TABLE 1 THE HYPOTHESIS OF THE DIFFERENTIAL RATE OF GENETIC OR BIOLOGICAL CONTRIBUTIONS FOR WHITES AND NEGROES ON SPATIAL TEST PERFORMANCE MUST BE REJECTED. THAT IS, ENVIRONMENT DOES NOT PLAY A MORE SIGNIFICANT ROLE IN THE MENTAL DEVELOPMENT OF SPATIAL ABILITY OF TEHE DISADVANTAGED (NEGRO) THAN OF THE CULTURALLY ADVANTAGED. THIS SPEECH WAS PRESENTED AT THE AMERICAN EDUCATIONAL RESEARCH ASSOCIATION CONVENTION, CHICAGO, ILLINOIS, FEBRUARY, 1968. (AUTHOR)