Many young adolescents are dissatisfied with their body due to a discrepancy between their ideal and actual body size, which can lead to weight cycling, eating disorders, depression, and obesity. The current study examined the associations of parental and peer factors with fifth-graders' body image discrepancy, physical self-worth as a mediator between parental and peer factors and body image discrepancy, and how these associations vary by child's sex. Body image discrepancy was defined as the difference between young adolescents' self-perceived body size and the size they believe a person their age should be. Data for this study came from Healthy Passages, which surveyed 5,147 fifth graders (51 % females; 34 % African American, 35 % Latino, 24 % White, and 6 % other) and their primary caregivers from the United States. Path analyses were conducted separately for boys and girls. The findings for boys suggest father nurturance and getting along with peers are related negatively to body image discrepancy; however, for girls, fear of negative evaluation by peers is related positively to body image discrepancy. For both boys and girls, getting along with peers and fear of negative evaluation by peers are related directly to physical self-worth. In addition, mother nurturance is related positively to physical self-worth for girls, and father nurturance is related positively to physical self-worth for boys. In turn, physical self-worth, for both boys and girls, is related negatively to body image discrepancy. The findings highlight the potential of parental and peer factors to reduce fifth graders' body image discrepancy.