Purpose: Self-stigma occurs when a person internalizes and applies stereotypes, prejudice, and discrimination to themselves. For adults who stutter, self-stigma is linked to negative outcomes and reduced quality of life. The development of self-stigma in people who stutter is not well understood. The aim of this study is to evaluate stuttering self-stigma in school-age children and adolescents and explore potential relationships to stuttering's overall adverse impact. Method: One hundred one children and adolescents who stutter, aged 10-18 years, completed the Overall Assessment of the Speaker's Experience of Stuttering (OASES), a measure of adverse impact related to stuttering, and the Childhood Self-Stigma of Stuttering Scale (Child 4S), our novel adapted version of the Self-Stigma of Stuttering Scale (4S) created for this study. The Child 4S comprises three subscales measuring three stages of self-stigma: Awareness, Agreement, and Application. Each stage was evaluated for relationships with child age and the adverse impact of stuttering. Results: We found a range of self-stigma scores among children and adolescents who stutter. Child age did not correlate with Awareness and Agreement; however, older children and adolescents reported greater Application. All stages of self-stigma strongly predicted adverse impact as measured by the OASES, and latter stages of the model were stronger predictors than earlier stages. Conclusions: Children as young as 10 years old may experience stuttering self-stigma, and the application of self-stigma increases in adolescence, a critical period in the development of personal identity. Importantly, all stages of self-stigma predicted adverse impact related to stuttering, with latter stages being stronger predictors than earlier ones consistent with the progressive model of self-stigma being tested. The findings highlight the need for targeted, early intervention to mitigate downstream effects of stuttering self-stigma.