This chapter reviews self-perception research, giving special attention to studies conducted with children in physical education. The relationships among various psychological factors and self-perceptions are explored, as well as how self-perceptions are related to motivated behaviors and physical activity participation. Developmental differences in perceptions of competence are predicted by competence motivation theory, and researchers have found that perceptions of academic competence decline with age. The self-perceptions of children with various disabilities have been examined, including learning disabilities and several types of motor coordination difficulties and obesity. The research indicates that students' self-perceptions may impact their physical activity participation, even if indirectly, by affecting other psychological or behavioral factors. The opposite also appears to be true; high levels of physical activity can lead to high self-perceptions. It is vital to students' activity levels that physical educators create an environment to enhance students' self-perceptions.