Using achievement goal theory as a theoretical framework, this study examined how children and adolescents conceptualized their own ability in physical education. Specifically, children and adolescents were asked to rate their own ability in physical education and to explain the basis for their rating. The research also aimed to identify children and adolescents who attained the differentiated conception of ability but believed in the efficacy of effort. Students (
N= 120) in 4th, 8th, and 11th grades were interviewed and completed a questionnaire. Results indicated that the criteria the children and adolescents used forjudging their own ability differed by grade. Children and adolescents at all grade levels tended to assess their own ability in terms of social comparison. Some adolescents with the differentiated conception of ability maintained a belief in the effectiveness of effort.