Errors of diagnostic reasoning contribute significantly to patient harm. Students, novice diagnosticians, and even experienced clinicians often have difficulty understanding or describing the processes of diagnostic reasoning. Inappropriate use of cognitive heuristics and poor logical reasoning by novice or experienced diagnosticians may result in missed or delayed diagnoses. Reduction of diagnostic errors through knowledge acquisition, self-reflection, and check lists has individually demonstrated some improvements in diagnostic reasoning. Implementing the diagnostic and reasoning tool (DaRT), a method of reasoning which integrates the evidence-based strategies of knowledge acquisition, metacognition, and logical reasoning skills throughout the patient encounter, results in improvement in diagnostic reasoning in advanced practice nurses. Use of the DaRT in one university setting resulted in significant improvement in advanced health assessment skills and diagnostic reasoning abilities as demonstrated by improvements of 28-55% end-of-program Health Education Systems Incorporated scores. Translation into practice settings may further support the use of this multiple-modality tool.