Building on my earlier studies of mechanistic reasoning, my current research is investigating development of reasoning about more complex biological mechanisms. My work focuses primarily on two populations – biology graduate students and undergraduates in upper division biology courses. Like their faculty mentors, graduate students are involved in the process of building and refining models. However, little is known about how these students learn to use model-based reasoning. Thus I am focused on defining the intermediate reasoning states between novice and expert researchers. Additionally, I am interested in exposing students to authentic biological reasoning at points earlier than graduate school. She is collaborating to develop a model for bringing the reasoning practices of biologists into an upper division undergraduate course. Research within this course will include describing the forms of reasoning that students reveal during small group problem solving sessions. Modern biologists employ a set of practices and reasoning skills that allow them to construct models of natural phenomena and refine these models through experimentation and hypothesis testing. Expert models of the phenomena they research are typically dynamic, detailed and full of causal connections. Model building is heavily connected to the physical and mental work biologists do in the laboratory. The formal and informal models that biologists use are highly productive tools for explaining and making predictions about the biological world. My interest is in understanding the development of these forms of reasoning and practice. Children begin to develop the skills for causal reasoning and explanation building at a young age, but how these early resources are fostered through schooling is not well understood. My earlier work demonstrated how school-age children constructed explanations for a simple visible system of levers. These studies suggested that even when all components of a mechanism are available for children to see and manipulate they often fail to explain the action of the system in terms of mechanism. In particular many children struggled to identify components relevant to mechanism, mentally animate the motion of the system, and build causal connections to explain the relevance of interactions within the system. However, my colleagues and I went on to show how careful instruction could help young students begin to understand and reason about these simple mechanisms.