Changes that occurred in the use of the dimensions of power and function were investigated in a cross-sectional study of second-born and only children aged five to 13 years. The investigation focused on age of child, sex of child, sex of sibling, age-spacing between sibling and sibling status of child. Results indicated that children significantly utilized these dimensions to discriminate sibling age- and sex-roles and that the presence of an older sibling facilitated the learning of power and function in social interaction. Sex of the sibling produced markedly different perceptions and discriminations of intersibship interaction. Age changes were prevalent in the use of these dimensions to discriminate sibling age- and sex-roles. The results were discussed in relation to previous investigations concerned with Parsonian theory of the family as a social system. (Author)