A collaborative study of Cultural Adjustment and Trauma Services (CATS), a comprehensive, school-based mental health program for traumatized immigrant children and adolescents, was conducted to generate practice-based evidence on the service delivery model across two school districts. Program effectiveness was assessed by testing whether client functioning and PTSD symptoms improved as a result of 7 separate service elements. An array of clinical services including CBT, supportive therapy, and coordinating services were provided to all students, and an evidence-based intervention for trauma, TF-CBT, was implemented with a subset of students. Greater quantities of CBT and supportive therapy increased functioning, while greater quantities of coordinating services decreased symptoms of PTSD. TF-CBT services were associated with both improved functioning and PTSD symptoms, although TF-CBT was implemented with fidelity to the overall comprehensive service model rather than the structured intervention model. Results suggest the comprehensive school-based model was effective, though different service components affected different student outcomes. Implications of these findings for immigrant mental health interventions and implementing structured evidence-based practices into community mental health programs are discussed. Suggestions are made for future research on existing mental health practices with immigrants.