What makes siblings different? The development of sibling differences in academic achievement and interests.

To illuminate processes that contribute to the development of sibling differences, this study examined cross-lagged links between parents' beliefs about sibling differences in academic ability and differences between siblings' grade point averages (GPAs), and cross-lagged links between differences in siblings' GPAs and sibling differences in academic interests. Data were collected from mothers, fathers, firstborn youth (M age at Time 1 = 15.71, SD = 1.07), and secondborn youth (M age at Time 1 = 13.18, SD = 1.29) from 388 European American families on 3 annual occasions. Findings revealed that, after controlling for siblings' average grades and prior differences in performance, parents' beliefs about sibling differences in academic ability predicted differences in performance such that youth rated by parents as relatively more competent than their sibling earned relatively higher grades the following year. Siblings' relative school performance, however, did not predict parents' beliefs about differences between siblings' competencies. Further, after controlling for average interests and grades, sibling differences in GPA predicted differences in siblings' interests such that youth who had better grades than their siblings reported relatively stronger academic interests the following year. Differences in interest, however, did not predict sibling differences in GPA. Findings are discussed in terms the role of sibling dynamics in family socialization.