ImportanceMore than 1 in 5 children in low-income families report a mental health (MH) problem, yet most face barriers accessing MH services. Integrating MH services into primary care at pediatric practices such as federally qualified health centers (FQHCs) may address these barriers.ObjectiveTo examine the association of a comprehensive MH integration model with health care utilization, psychotropic medication use, and MH follow-up care among Medicaid-enrolled children at FQHCs.Design, Setting, and ParticipantsThis retrospective cohort study used Massachusetts claims data from 2014 to 2017 to conduct difference-in-differences (DID) analyses before vs after implementation of a complete FQHC-based MH integration model. The sample included Medicaid-enrolled children aged 3 to 17 years who received primary care at 3 intervention FQHCs or 6 geographically proximal nonintervention FQHCs in Massachusetts. Data were analyzed in July 2022.ExposuresReceipt of care at an FQHC implementing the Transforming and Expanding Access to Mental Health Care in Urban Pediatrics (TEAM UP) model, which began fully integrating MH care into pediatrics in mid-2016.Main Outcomes and MeasuresUtilization outcomes included primary care visits, MH service visits, emergency department (ED) visits, inpatient admissions, and psychotropic medication use. Follow-up visits within 7 days of a MH-related ED visit or hospitalization were also examined.ResultsAmong the 20 170 unique children in the study sample, at baseline (2014), their mean (SD) age was 9.0 (4.1) years, and 4876 (51.2%) were female. In contrast to nonintervention FQHCs, TEAM UP was positively associated with primary care visits with MH diagnoses (DID, 4.35 visits per 1000 patients per quarter; 95% CI, 0.02 to 8.67 visits per 1000 patients per quarter) and MH service use (DID, 54.86 visits per 1000 patients per quarter; 95% CI, 1.29 to 108.43 visits per 1000 patients per quarter) and was negatively associated with rates of psychotropic medication use (DID, −0.4%; 95% CI −0.7% to −0.01%) and polypharmacy (DID, −0.3%; 95% CI, −0.4% to −0.1%). TEAM UP was positively associated with ED visits without MH diagnoses (DID, 9.45 visits per 1000 patients per quarter; 95% CI, 1.06 to 17.84 visits per 1000 patients per quarter), but was not significantly associated with ED visits with MH diagnoses. No statistically significant changes were observed in inpatient admissions, follow-up visits after MH ED visits, or follow-up visits after MH hospitalizations.Conclusions and RelevanceThe first 1.5 years of MH integration enhanced access to pediatric MH services while limiting the use of psychotropic medications. Additional implementation time is necessary to determine whether these changes will translate into reductions in avoidable utilization.