provide the kinds of feedback that help them develop a systematic catalogue of those conceptions and a repertoire of productive approaches to addressing them. Experiences that provide this kind of information at the appropriate level of detail to guide instruction are particularly important to understand. This research would clearly support efforts to understand teacher knowledge requirements in other subject matter, with very close parallels, for example, to the teacher knowledge agenda in reading comprehension.
It would surely be disturbing if the mathematics instruction in schools followed no plan for increasing students’ knowledge cumulatively across grades of study but instead meandered from topic to topic in an unprincipled way. Yet this is an accurate description of science instruction in elementary schools and in many middle schools. High schools have a more predictable sequence of science subjects rooted in tradition, but the subjects are generally treated separately. Even in high school, there is little effort devoted to drawing connections in the content across subjects or to systematically building an understanding of the discipline.
Achieving consensus on the content of science education across the K-12 school years has been stymied by a long history of debates and subsequent confusion about the appropriate organizing principles for science education. The debates often swell around the process-content divide. Some have argued that the most important thing for students to learn is the process of scientific reasoning, including the logic of controlling extraneous variables in scientific experimentation, the coordination of theory and evidence, and standards for evaluating evidence. However, these attempts often founder on superficial and fragmented treatments of science content. Too exclusive an empha-