An examination of how new knowledge is acquired reveals that knowledge is organized in global conceptual constructs called schemata, and that the process of knowledge acquisition can be conceptualized as the articulation and restructuring of these schemata. Assuming that a schema is a generative structure with implications beyond what is immediately known, the working out of these implications is schema articulation. Schema restructuring is the kind of learning that involves fundamental changes in the nature of the schema itself. The domain of observational astronomy (i.e., the knowledge about the sun, moon, and stars in relation to the earth) would be an appropriate domain to test these ideas. When the purpose of instruction is to promote schema articulation, it is important to build instruction around the child's already existing schema. When the purpose of instruction is to promote knowledge restructuring, it is important to foster recognition of the anamolies in the existing schema and to use explanatory analogies and/or physical models to bring relevant knowledge from a different domain to help schema restructuring. An 11-page reference list is appended. (EL)