Students come to our physics classes with preconceptions. As active, learning human beings, they have naturally attempted to make sense of the world around them. But, this sense is not the same as the ideas and reasoning of formal science. Most instruction does not address these preconceptions, so for many students, the initial ideas do not change as a result of experience in our physics classes. Students memorize school science and keep their personal sense without changing it appreciably. We have organized the various student conceptions into what we call ”facets” of thinking. We identify their initial ideas at the beginning of a unit. Now as we design our curriculum activities, our assessment tasks, and our teaching strategies, we are using the students initial thinking as targets for instruction. Their ideas are the hypotheses that students will test against the experiences we put before them in benchmark lessons, elaboration lessons, and application activities. Assessment, including diagnosing their developing facets of thinking, is embedded within subsequent instruction and used at the end of instruction. Using instruction that specifically diagnoses and addresses students thinking is yielding very positive results for the teachers and students working with us.