GENDER OF SIBLINGS, COGNITIVE ACHIEVEMENT, AND ACADEMIC-PERFORMANCE -FAMILIAL AND NONFAMILIAL INFLUENCES ON CHILDREN

In this article, I use data on twins to obtain estimates of the degree of shared familial influence on cognitive achievement and academic pe rformance. The results indicate that there is considerable shared infl uence on cognitive achievement but much less for academic performance. The model estimated also indicates a considerable degree of sibling s ymmetry in both outcomes. The only significant difference rests betwee n opposite-gender twins. For these twins, nonshared sources of influen ce are more important than for same-gender twins. Finally, the results indicate that the regression of academic performance on cognitive ach ievement is not biased by unmeasured familial characteristics.