The system model of evaluation is preferable to the traditional goal attainment model because it offers more promise for programmatic use of the evaluation findings, being designed to consider the operations and goals of the entire organization rather than having a narrow focus on a particular goal singled out of context. The systems model also recognizes the dynamic process of goal implementation without holding the program steady in an arbitrary way. The research at Tegel Prison compared the relative effectiveness of orthodox penal confinement and therapeutic intervention within the facility and compared the relative effectiveness of three treatment models -- the social therapy model, the school model, and the social training model. The study began in 1976 and data collection concluded in May 1978. Selected for study were 1,503 released prisoners, comprising 6 experimental groups who had completed or been enrolled in 1 of the 3 program models and four control groups without therapeutic experience. The study concluded that the establishment of the social therapeutic unit cultivated a therapeutic philosophy throughout the prison and inmates exposed to it had lower recidivism rates. The therapeutic models were found not to differ significantly in outcome when measured by reconviction rates. The evaluation proceeded on the assumption that the ultimate research product would delineate the most appropriate place and functions of the therapeutic unit within the prison as a whole, maximizing the evaluation's potential for contributing to the ultimate purpose of moving West German prisons toward the therapeutic orientation. The use of the system model made the research findings acceptable to administrators and policymakers; attention was focused on the problem to be overcome rather than on validation of a particular possible solution. Nine references are given.