Although constructivism is a concept that has been embraced by many teachers over the past 15 years, the meanings that are attached to this term are varied and often inadequately understood. Teachers need to have a sound understanding of what constructivism means to evaluate its promise and to use it knowledgeably and effectively. This paper explicates some of the theoretical background of constructivism and then presents a detailed example in which a traditional classroom lesson and a constructivist version of the same lesson are described and analyzed. Also discussed are pervasive myths and important instructional issues of this widely advocated and increasingly popular philosophical framework for teaching across the entire K-12 curriculum.