The widely reported “epidemic of medical error” has resulted in calls to find systems that prevent, detect, and correct errors. Our incident investigations indicated that specimen-processing personnel often facilitated negative patient outcomes by failing to prioritize work or modify rules in critical situations. Our team developed a knowledge and problem-solving assessment for specimen-processing personnel in order to identify opportunities for training. We included a self-assessment and found that poor performers grossly overestimated their knowledge and problem-solving ability. This study illustrates the utility of using competency challenges to identify opportunities for improvement.