Concepts are not the same as conceptions, and so conceptual change differs from conceptional. Concept has at least two meanings, one of classification and one of the set of knowledge the person associates with the concept's name. Conceptions are different again; they are systems of explanation. Teachers are skilled at promoting conceptual change, of either sort. Conceptional change is more difficult, and requires procedures such as metacognition and new forms of assessment that promote recognition and resolution of conflict between conceptions.