My research project is about testing ways to improve the clinical reasoning education for general practitioners in training. In three studies, we tested different ways to teach them a procedure to engage in more analytical, reflective reasoning when diagnosing cases. Previous studies have found, that this Deliberate Reflection procedure can help physicians to correct diagnostic mistakes, that they may make initially. We tested different types of interventions, which were learning-by-doing, example-based learning, and learning-by-teaching. In a fourth study, we tested whether we could help general-practitioners in training to better estimate how well they have diagnosed a case. Reducing overconfidence in a wrong diagnosis or underconfidence in a correct diagnosis, could help them to make less errors in clinical practice. However, this intervention proved to be ineffective.