The process of conceptual change, in learners and in scientific knowledge, indicates that: (1) change involves complex and varied commitments to methods of investigation, aims and goals of investigation, and prior knowledge; (2) change leads to consensus forming or dissensus forming activities; (3) knowledge claims and procedures for testing knowledge claims are not held to be equally important by individuals; and (4) anomalous data play an important role in bringing about changes to commitments and fostering either consensus or dissensus forming activities. Historical episodes of the development of theory, method, and aim commitments within a specific scientific domain are the way these four indicators can be incorporated into a science curriculum. The relationship between the intended curriculum and the implemented curriculum is described. A principled reasoning curriculum can be designed using frameworks from the history and philosophy of science that describe knowledge change. (KR)