The authors applied contemporary methods from the evaluation literature to measure implementation in a residential treatment program for adolescent substance abuse. A logic model containing two main components was measured. Program structure (adherence to the intended framework of service delivery) was measured using data from daily activity logs completed by program staff. Treatment process, conceptualized as therapeutic milieu, was measured using an adapted version of a scale used to measure implementation in therapeutic communities. In addition, variability in implementation was measured using statistical process control (SPC) procedures. Adolescents completed, on average, 50% of the weekly prescribed services. The milieu of the program was rated by the adolescents as highly therapeutic. Moreover, preliminary psychometrics suggest therapeutic milieu can be measured reliably in adolescents. These two main variables were implemented with consistency across adolescents. These findings are discussed along with implications for evaluation work in similar fields.