The ability to interpret and apply experiences, or cases (Kolodner, 1993; 1997) is a skill (Anderson, et. al, 1981; Anderson, 2000) that is key to successful learning that can be transferred (Bransford, Brown and Cocking, 1999) to new learning situations. For middle-schoolers in a project-based inquiry science classroom, interpreting and applying the experiences of experts to inform their design solutions is not always easy (Owensby and Kolodner, 2002). Interpreting and applying an expert case and then assessing the solution that results from that application are the components of a process I call case use. This work seeks to answer three questions: 1. How do small-group case use capabilities develop over time? 2. How well are students able to apply case use skills in new situations over time? 3. What difficulties do learners have as they learn case use skills and as they apply case use skills in new situations? What do these difficulties suggest about how software might further support cognitive skill development using a cognitive apprenticeship (Collins, Brown and Newman, 1989) framework? I argue that if learners in project based inquiry classrooms are able to understand, engage in, and carry out the processes involved in interpreting and applying expert cases effectively, then they will be able to do several things. They will learn those process and be able to read an expert case for understanding, glean the lessons they can learn from it, and apply those lessons to their question or challenge. Furthermore, I argue that they may also be able to transfer interpretation, application, and assessment skills to other learning situations where application of cases is appropriate.