This chapter focuses on the changes in the mathematical knowledge and understanding of one student as she explored a particular mathematical topic area (the graphs and equations of simple algebraic functions in the Cartesian plane) for a period of 7 hours spread intermittently over 7 weeks. It provides a fine-grained characterization of her knowledge structures related to the domain and a description of the nature of the change in those knowledge structures as a result of her interactions with the learning environment. That is, it describes, in fine detail, how and what the student learned as she came to grips with a complex body of mathematics.