The resurgence of support for offender rehabilitation has led to an increased emphasis on correctional program integrity. Treatment programs are now being evaluated and tailored in accordance with the principles of effective intervention, which are rooted primarily in methods of individual behavior modification through a social learning approach. The problem with this exclusive focus on the individual is that it fails to recognize the importance of certain ecological factors that have been shown to be significant predictors of recidivism. The purpose of the current research, therefore, is to examine the impact of structural characteristics on both treatment program quality and effectiveness of halfway house programs in Ohio. The results reveal that ecological context influences the magnitude of program treatment effects largely indirectly though its influence on program quality. The implications of these findings for correctional theory and practice are discussed. Abstract published by arrangement with Taylor and Francis.