Preventive education and birth order as co-determinants of IQ in disadvantaged 5-year-olds.

The effects of preventive education and birth order on IQ scores of 95 economically disadvantaged children at risk for retarded intellectual development were studied. Experimental first- and later-born children participated from birth in a 5-year programme of systematic educational intervention. An equal number of children served as controls and received no systematic intervention. First-borns prevailed as the brighter children in both the educational treatment group and the control group when Wechsler Preschool and Primary Scale of Intelligence (WPPSI) full scale and verbal IQ scores were compared. Furthermore, mothers of first-borns (70% of whom were only-born at age 5) achieved significantly higher WAIS scores than did mothers of later-born children. Results suggest that later-born disadvantaged children are at greatest risk for developmental retardation.