In a study based on data collected by Project TALENT, only children and individuals from two-child families were compared on a number of outcome variables in order to explore whether, and in what way, only children differ from children with siblings. A sample of 3221 Project TALENT participants who were in either the ninth or twelth grade in 1960 and who responded to a follow-up survey conducted 11 years after their expected date of high school graduation was selected. This sample, which was stratified on socioeconomic status, was approximately equally divided between males and females. Within each of these four grade/sex subsamples were approximately equal numbers of only children and individuals from two-child families. This sample was, in turn, further limited to persons living with both of their parents in 1960. Independent analyses were carried out within each of the grade/sex subgroups using a set of 131 dependent variables. These dependent variables, which were collected in either 1960 or at the time of the 11-year follow-up survey, were organized into 10 categories: cognitive abilities, personality characteristics, occupational interests, social life, health, activities, education/academic achievement, marriage and childbearing, work and mobility. Although significant differences were found between only children and individuals from two-child families on eight of the above ten categories (no differences were found in terms of health and mobility), none of these differences was found to be large in absolute terms. (Author/MP)