Mandibular advancement represents one of the therapeutic approaches for the treatment of skeletal Class II malocclusions in adolescent patients, taking advantage of the residual growth potential characteristic of this stage of development. Numerous longitudinal studies and systematic reviews have analyzed the effects of functional appliances, both removable and fixed, on the craniofacial complex, highlighting differences in mechanisms of action, the magnitude of skeletal and dentoalveolar effects, and long-term stability. The literature shows that removable functional appliances, such as activators and the Twin Block, are more effective when used close to the pubertal growth peak. However, the clinical effectiveness of these appliances is dependent on patient cooperation. Fixed mandibular advancement devices, including the Herbst appliance, Forsus, and similar systems, provide continuous and controlled advancement, thereby reducing the compliance variable. This presentation offers a critical review of the available evidence, with particular attention to treatment timing, the distinction between true skeletal effects and dentoalveolar compensations, and the long-term stability of treatment outcomes. Clinical criteria for selecting the most appropriate appliance in relation to biological age, growth pattern, and severity of the sagittal discrepancy are also discussed. In conclusion, the literature supports the use of mandibular advancement in adolescents as an effective treatment, provided it is implemented within an appropriate temporal framework and planned on the basis of an individualized patient assessment.