The relationship between self-concept and level of cognitive development were examined. It was hypothesized that level of cognitive development would predict self-concept response style, and that less cognitively mature young adolescents would have higher self-concept scores. The original subjects were 91 seventh graders who responded to two objective self-concept scales, to Piaget's pendulum and balance beam problems, and to a permutation problem. The data, analyzed by a multiple regression technique, indicated that cognitive level was a significant predictor of self-concept response style. Multivariate ANOVA's provided support for the remaining hypotheses. The less cognitively mature seventh-grade children scored higher on self-concept. A follow-up investigation of participants classified as both concrete thinkers and as extreme responders was conducted six months later and provided additional support for the hypotheses. These results were discussed in terms of changes in self-perceptions with increasing cognitive ability, the use of self-report scales with young adolescents, and the possibility of developing a theory of self-concept which includes Piagetian notions about the development of knowledge. (Author)