The purpose of this study is to explore the knowledge demands of teacher educators as they teach disciplinary content to preservice elementary teachers, specifically in mathematics, and to understand how such knowledge is different from that used by K-12 teachers. Drawing from a database including teaching and learning artifacts from five iterations of a content course for preservice teachers, the authors illustrate different forms of knowledge observed across different mathematics teacher educators' practice and discuss how the observed knowledge forms are different from knowledge used by K-12 teachers in their practice. Finally, the authors discuss how the process used in this study can identify potential components of a knowledge base for teacher education.