The increasingly connected and technologically mediated world both gives learners unprecedented access to data about complex systems, and simultaneously requires increasingly sophisticated STEM reasoning skills to grapple with those complex systems. This project will develop analytical tools, simulations, and online learning materials to help adult learners make sense of the complex systems involved in Type 1 Diabetes (T1D). The project will use the context of T1D to develop a model for how people engage in complex systems sensemaking with real-world incomplete data, and will examine how learners make use of the simulation tool to develop the STEM skills of data interpretation, understanding relationships between variables, and the role of uncertainty. Lessons learned from this project will both inform the further development of supports for this specific learner community, as well as inform supports that other adult learner communities might need to learn about complex systems in their day-to-day lives. The project will develop the sensemaking model by exploring the following research questions: (1) how people with T1D make sense of uncertain, real-time data along with dozens of other factors to help them learn the STEM knowledge and skills related to their chronic illness; (2) what features online materials need in order to best serve the STEM knowledge and skill gaps that people with T1D face when learning about their chronic illness; and (3) what ways a simulation can