The revised standards used by the National Council for Accreditation of Teacher Education (NCATE) embody several departures from past standards. One difference is that they oblige units to focus on the knowledge bases pertinent to professional preparation for education. The concept of knowledge bases is explored, and implications for the construct validity of the NCATE assessment process are examined. To pin down exactly what is meant by knowledge bases is a difficult task, and to demand that units structure their programs around knowledge bases is equally difficult. It is implicit in the standards that explicit knowledge bases are a necessary characteristic of quality programs, but there is no research to support the idea that programs based on explicit knowledge bases necessarily produce better teachers than do programs with no explicit knowledge base. The current reliance of the NCATE process on the construct of knowledge bases prompts doubts and highlights the need for an increase in conversation about the construct validity of the NCATE process itself and inferences drawn from it. Eighteen references are included. (SLD)