Infants judged to be at risk for subnormal intellectual growth were randomly assigned to an experimental (N=27) or a control (N=25) group. Infants in both groups received medical care and dietary supplements; their families received social work services on a request basis. Experimental children participated in an educational day care program beginning before the third month of life. The day care program was composed, in part, of curriculum activities designed to stimulate intellectual growth. Between 6 and 36 months of age, experimental children maintained normal intellectual growth; control children declined in IQ beginning between 12 and 18 months of age and remained significantly lower than experimental children at 24 and 36 months. The mother-child IQ correlation for control dyads was .43; for experimental dyads the correlation was -.05. These two types of evidence are interpreted as support for the importance of early environments in the development of intelligence. (Author/RH)