Background and objectives: Despite substantial global burden of mental illnesses, there remains limited evidence evaluating the effectiveness of inpatient Models of Care (MOC) for adolescents. This paper compares the effectiveness of an innovative MOC, the Brief Intervention MOC (BIMOC), with the Traditional MOC in the acute adolescent inpatient unit. Comparisons were based on clinical outcome measures and several Key Performance Indicators (KPIs) (Length of Stay, 28-day readmission rate, 7-day follow-up rate, seclusion rate, and self-harm incidents), which were tracked over the subsequent years to evaluate BIMOC’s effectiveness and sustainability. Materials and Methods: A quasi-experimental design was applied. Clinical outcomes were assessed using the Health of the Nation Outcome Scales for Children and Adolescents (HoNOSCA) and the Children’s Global Assessment Scale (CGAS).Service-level KPIs were compared across models. Descriptive statistics, paired-samples t-tests, Cohen’s d, and z-tests were used to evaluate changes within models and compare outcomes between models. Results: Within the BIMOC, both acute and crisis subgroups showed substantial improvements, with increased CGAS scores and corresponding reductions in HoNOSCA scores. Overall, both models demonstrated significant improvements; however, effect size analysis indicated greater functional gains under the BIMOC compared with the TMOC, while symptom improvements were comparable between two MOC. KPI data analysis demonstrated sustained improved service performance under the BIMOC compared to the TMOC. Conclusions: The study implies that a structured and integrated inpatient MOC( BIMOC), can deliver comparable clinical outcomes while improving efficiency, safety, and continuity, highlighting its potential as a sustainable solution for high-demand adolescent mental health services.