Introduction: Building Knowledge Bases and Improving Systems of Practice

In the introductory essay to this special issue, we argue that a knowledge base for teacher education will grow only if the field attends directly to the processes used to study and improve its practices. We identify 4 features that characterize the processes used by a diverse set of outside-of-education systems to build knowledge for improving professional practice: shared goals across the system; visible, tangible, changeable products; small tests of small changes; and multiple sources of innovation from throughout the system. Our intent in describing these features is to set the stage for examining how knowledge can be built for educating (mathematics) teachers, a challenge addressed in this article and those that follow in this special issue.