The Intellectual Achievement of Only Children

Summary A quantitative review of the literature on the intellectual achievement of only children indicated that only children were never at a disadvantage in relation to any comparison group; nor were they significantly different from first-born children or children from two-child families. Moreover, only children were at a significant advantage in comparison with later-born children and those from large families. The consistency of these findings across subgroups suggests that interpersonal mechanisms are largely responsible. The strong only-child advantage on tests of verbal ability, together with the overall pattern of findings, implicates parent–child interactions as responsible for the family size and birth order variations in intellectual achievement.