Measurement feedback systems (MFSs) that routinely collect and report client progress to mental health therapists have demonstrated beneficial impact on outcomes in numerous studies, with evidence that there is a dose-response relationship related to the implementation of the MFS. The current study examined the impact of MFS implementation (Implementation Index) on youth symptom outcomes separately by caregiver and youth self-report. Additionally, we tested the extent to which Implementation Index rates varied by individual therapists and clients, and whether therapist and client characteristics predicted MFS implementation. Methods: Administrative data (client charts, youth- and caregiver-reported Youth Outcome Questionnaires) for 229 youth (52.83% Latinx, 42.79% girls, M age = 10.33) treated during a 1-year period at a community mental health organization in Central Texas were analyzed using multi-level modeling. Caregiver-reported symptoms decreased faster for those with a higher MFS Implementation Index. Between-group differences among therapists accounted for a significant proportion of variance in the Implementation Index for caregiver report, whereas client differences accounted for most of the variance in the Implementation Index for youth self-report. Therapist trainee status predicted a significant increase in the Implementation Index for caregiver-report data. Youth symptom improvement as reported by caregivers varied with the extent of MFS implementation fidelity, and MFS implementation fidelity was higher for clients treated by trainees relative to staff therapists for caregiver report of symptoms.