Sleep plays a crucial role in energy balance, alongside diet and physical activity. Research has linked poor sleep quality and short sleep duration to obesity and cardiometabolic risk, such as insulin resistance and hypertension. The nature of this association is complex, and several mechanims have been suggested. Scientific evidence suggests that sleep interventions may provide additional benefits in optimizing the effectiveness of overweight/obesity treatment in pediatric populations. Although some studies have explored this hypothesis, methodological heterogeneity hampers clear interpretation of the results. The main goal of this clinical trial is is to evaluate the efficacy of a sleep behavioral intervention, combined with standard obesity treatment, in reducing adiposity (measured by BMI z-score, fat mass percentage, or fat-free mass index) in adolescents with overweight or obesity. This randomized controlled trial will compare a control group receiving treatment as usual (or standard obesity treatment) with an intervention group receiving treatment as usual plus a sleep behavioral intervention. Participants will be randomized into two groups: intervention and control. Throughout the study period, all medical consultations will include standard interventions focused on nutrition, physical activity/sedentary behavior, and other lifestyle factors. The sleep-focused intervention will be delivered by psychologists. Participants will attend clinic visits every two months during the 6-month intervention period, and every three months during the subsequent 6-month follow-up period.