Four decades ago David Ausubel made the oft-quoted statement: "The most important single factor influencing learning is what the learner already knows. Ascertain this and teach accordingly." But for four decades, we have been trying to find out what accordingly means! K-12 students (and teachers) hold strongly held ideas about the natural world as they try to make sense of their every day and instructional experiences. Teaching for conceptual understanding involves building a bridge between students' initial ideas and the core scientific ideas we want all students to know and be able to use.
