In this article, the authors report a study into the Dutch probation service about the question whether structured decision making about case management plans does or does not improve the quality of these plans, and subsequently improves the effectiveness of offender supervision. Two samples of nearly 300 case management plans each were compared. In the first sample a tool for risk/needs assessment was used to assess the risks and needs but decision making about the subsequent case management plan was not structured (RISc2-sample). In the second sample professionals used the same tool for risk and needs assessment but now it also contained a section for structured decision making about the case management plan (RISc3-sample). Results showed that in the RISc3-sample the quality of the plans was significantly better than in the RISc2-sample: a better match between criminogenic needs and goals, a better match between goals of the offender and goals in the plan, more focus on strengthening social bonds, and a better match between risk of recidivism and intensity of the plan. Some significant correlations between the quality of the plans and the effectiveness of offender supervision were found, indicating that improving case management plans by structured decision support indeed can contribute to probation practice.