The influence of sibling structure on cognitive and sociomoral development during middle childhood and early adolescence

The influence of sibling structure on cognitive and sociomoral development is examined against the background of cognitive-structural theory and research (Piaget, Kohlberg) and theoretical assumptions of the cultural-historical school (Vygotsky). Subjects (N = 121 from Reykjavik/Iceland) were tested longitudinally at ages 7, 9, 12, and 15 years. Cognitive development was assessed by a battery of Piagetian tasks, sociomoral development by an interview about an everyday moral dilemma. Analyses revealed significant main effects of age difference and interaction effects of age difference with sex of next-older sibling. Subjects with a sister at least four years older showed higher developmental levels compared to subjects with a sibling up to three years older. Subjects with a brother at least four years older, eldest and single childs scored between these two groups. Although sibling relationships with a small age difference are characterized by more intimacy and less status differences, cognitive and sociomoral development is fostered to a greater extent by a cognitive and socially more competent older sister.