Problem-based learning focuses on small groups using authentic problems as a means to help participants obtain knowledge and problem-solving skills. This approach makes problem-based learning ideal for teaching lean manufacturing, which is driven by a culture of problem solving that values learning as one key output of manufacturing production. Thus, simulations that organize participants in teams for realistic manufacturing production problem solving are widespread as a way to use problem-based learning to teach lean manufacturing. But a critical assessment of existing simulations for lean manufacturing instruction has been lacking. Accordingly, a literature survey is conducted and existing simulations are classified according to their emphasis on lean tools or the overall lean system; the degree of their focus on soft skills, if any; and their area of application, whether academic or industry. Four gaps are found in existing simulation designs: lack of stress on soft skills, a mistaken focus on "linear lean," misunderstanding of the key role of the facilitator, and lack of realism. Future directions for study and improvement in lean simulation design are suggested. (Contains 5 tables and 4 figures.)