We examine the argument that teaching will be more effective if adapted to individuals--what we call the interaction/adaptation hypothesis. What is likely correct about this hypothesis (but needs more research) is that modality of instruction may need to be adapted to certain types of content (e.g., geometry vs. literature) or to domain of objectives (e.g., cognitive vs. psychomotor). What is also correct (and has much empirical support) is that instruction needs to be adapted to the learners' prior knowledge and experience vis-a-vis the material to be learned. What is incorrect is that instruction should be adapted to learners' styles. We describe some of the major historical conceptualizations of adapting to individual differences, including summaries of the empirical evidence on these approaches. Finally, we offer an alternative approach--namely adapting to individuals' prior knowledge. (Contains 1 table, 1 figure, and 4 notes.) [Note: The publication year (2009) shown on the PDF is incorrect. The correct publication year is 2008.]