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 develop ment is examined against the background of cognitive-structural theory and research (Piaget, Kohlberg) and theoretical assumptions of the cu ltural-historical school (Vygotsky). Subjects (N = 121 from Reykjavik/ Iceland) were tested longitudinally at ages 7, 9, 12, and 15 years. Co gnitive development was assessed by a battery of Piagetian tasks, soci omoral development by an interview about an everyday moral dilemma. An alyses revealed significant main effects of age difference and interac tion effects of age difference with sex of next-older sibling. Subject s with a sister at least four years older showed higher developmental levels compared to subjects with a sibling up to three years older. Su bjects with a brother at least four years older, eldest and single chi lds scored between these two groups. Although sibling relationships wi th a small age difference are characterized by more intimacy and less status differences, cognitive and sociomoral development is fostered t o a greater extent by a cognitive and socially more competent older si ster.