Decision-support systems provide a large functionality sup-porting the decision making process. They allow to draw conclusions from data provided by users. In order to be applied they require however that the user is knowledgeable and knows how to interpret and apply the solutions provided. Often people need, however, an additional in-sight into the foundation of decision support systems. The Data Mining Tutor (DaMiT) has been developed in order to overcome this problem. The learning process is based on data provided by DaMiT and data pro-vided by users. User learn with the DaMiT system what kind of decisions can be made, what kind of conclusions might be drawn, and what kind of decisions should not be drawn due to the data quality.