School achievement records of 129 pairs of firstand second-born siblings from 2 school systems were analyzed. Siblings were compared on teacher grades and Iowa Basic Skill scores obtained during common years in their school careers (upper elementary and junior high). Differences between siblings on grades and test scores significantly favored the first-borns. The data also indicated that first-born superiority may be more pronounced for siblings close in age and for first-born girls.
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Chittenden et al. (1968) studied this question.