The objective of this study was to understand the relationship between an adolescent's older sibling and peers on their academic achievement applying Bowlby's attachment theory. Data for this study originated from Wave 1 (1989), Wave 2 (1990), and Wave 4 (1992) of the Iowa Youth and Family Project (IYFP). This study utilized a sample of 217 adolescents and their older siblings to predict adolescent's academic achievement.

Structural equation modeling (SEM) analyses estimated the relationship positive older sibling warmth and support had on an adolescent's closeness to peers and their academic achievement. This study partialed out demographic characteristics that can predict an adolescent's academic achievement. The results of this study substantiate previous findings revealing that positive warmth and support from an older sibling directly influences an adolescent's academic achievement.

This study failed to find peer relationships mediating positive older sibling warmth and support and academic achievement. Observed older sibling warmth and support significantly increased academic achievement but failed to increase closeness to peers. However, this study found a significantly indirect effect that indicated, through self-reported measures, when the target adolescent felt high warmth and support from their sibling, there was a positive effect on closeness with peers which resulted in an increase in academic achievement.