a1 Humanalysis, Saratoga Springs, New York
a2 University of Texas, Austin, USA
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.
(Received June 18 1987)