This study compared the effectiveness of two knowledge management system designs in supporting individual decision makers in a predictive judgement task. The black-box versus white-box system design was varied to allow for automating versus informating support in cue weighting and combination stages of the judgement process. The main findings indicate that only the white-box system design was effective in improving decision makers’ performance through enhancing their knowledge and debiasing their judgement strategies. However, the study reveals room for further improvement and provides directions for future research.