Treatment focus diffusion (TFD), dividing focus across multiple concerns during treatment, is common in public mental health care and differs from the more narrowly focused empirically supported treatments for youth reported in the literature. The present study examined whether and to what extent TFD is associated with youth functional improvement over the course of therapy. Method: This study utilized multi-level modeling techniques to analyze 12 consecutive years of standardized routine clinical service data from youth receiving treatment in one of two intensive in-home service settings: (a) Multisystemic Therapy (MST; n = 776 youths, 99 therapists), an implemented evidence-based treatment based on ecological theories of behavior in which therapists work with the multiple systems a youth interacts with (school, community, family), and (b) a standards-based service (n = 1854 youth, 413 therapists). Both service settings operate in the context of a publicly funded mental health care system which serves youth and families who are typically from underserved and low-income backgrounds. Majority of youth in this sample identified as multi-ethnic and male, and they, on average, were approximately 13 years old with three co-occurring diagnoses. Results: A significant TFD by service format interaction on youth functional improvement (alone and in the overall model) and follow up simple effects indicated that higher TFD was associated with significantly poorer outcomes in MST. The parameter estimate for TFD on functional improvement in the standards-based service format was in the same direction, but not statistically significant. Conclusion: Our findings suggest that maintaining a narrower treatment focus might be beneficial to clients, particularly in implemented evidence-based treatments. Likewise, TFD could be a helpful case monitoring tool for clinicians, supervisors, and systems leaders when reviewing intensive-in-home cases.