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. 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. 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. 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. https://doi.org/10.23641/asha.26352556.