Adolescents living with HIV (ALH) have poorer adherence to antiretroviral therapy (ART) than adults. Many ALH in sub-Saharan Africa (SSA) are enrolled in boarding schools where stigma is pervasive and may impact adherence. We collected sociodemographic data, school information, medical history, and viral load (VL) data from ALH age 14-19 in 25 HIV clinics in 3 counties in Kenya. Using generalized estimating equations, we compared ART adherence in ALH attending day and boarding schools. Of 880 ALH, 798 (91%) were enrolled in school, of whom 189 (24%) were in boarding schools. Of those in school, median age was 16 (IQR: 15, 18), 55% were female, 78% had a parent as a primary caregiver, and 74% were on DTG-based ART. Median age at ART initiation was 6 years (IQR 3, 10).Overall, 227 (29%) ALH self-reported missing ART when school was in session (40% in boarding and 25% in day school). After adjusting for sociodemographic and HIV care characteristics, ALH in boarding schools were significantly more likely to self-report missing ART than those in day schools (adjusted Prevalence Ratio (aPR): 1.47, 95% CI 1.18, 1.83, p=0.001). Among 194 ALH, only 60% had undetectable (<20 copies/ml) HIV viral load (62% day schools and 51% boarding schools)(p=0.097). ALH had high self-reported non-adherence overall, with worse adherence among those in boarding schools. Schools remain a critical untapped resource for improving ALH outcomes.