The increased sentence length for violent offenses has yielded an increasing proportion of violent inmates in the prison population. Prison itself is a debilitating and stigmatizing experience. If the aim is to reintegrate offenders into society and to reduce the level of violence, constructive and imaginative interventions must be developed. During the 1980s a number of promising initiatives were introduced in prisons on both sides of the Atlantic, but they were often erratic and short-lived and, for the most part, were not subject to systematic evaluation. The Cognitive Skills Program, which was developed in Canada, has been touted as a good example of a well-designed, effective, and properly evaluated program. The achievements claimed on its behalf have persuaded the Prison Department in England and Wales to adopt this general approach and to make it a central part of their rehabilitative strategy. A critical examination of the program and its evaluation reveals, however, that there are not only serious flaws in its conceptualization, but also in the way that it has been implemented. The major failing of the evaluation is that it shows little about what works and even less about how it works. There is no real examination of the causal processes at work, and the primary criteria for success, recidivism, remains an imprecise and uncertain measure. Rather than continue to evaluate programs primarily in terms of recidivism, as occurs in the majority of cases, this paper suggests that it is necessary to develop a range of realistic intermediate measures that combine quantitative and qualitative data through the use of extensive and intensive forms of research. In this way, it is possible to identify causal mechanisms and to examine their operation within various contexts. Finally, it is necessary to stop viewing correctional policy as a matter of finding a given program that has yielded promising evaluation findings. The interactive nature of the rehabilitation process and personal change is dynamic and depends on the motivation and qualities of both program staff and participants. 1 figure and 30 references