This paper reviews several studies on aptitude treatment interaction, the interaction between the learners' individual differences and methods of instruction. Specifically, it investigates the relationship between previous knowledge, including previously held misconceptions, and instructional methods. It is suggested that significant interactions are not easy to achieve. However, one reported study describes the positive interaction between low initial ability or prior knowledge and teaching methods that provide much instructional support (e.g. cues, structure, feedback, etc.). Interaction between learning styles and teaching method is also discussed, specifically a study in which instruction including use of metaphors was helpful to students with a preference for a visual format (visualizers) but not to those with a preference for a verbal format (verbalizers). The article advocates a metacognitive approach to evaluating learning, analyzing the cognitive processes involved in the learning rather than just the outcomes. It also proposes the use of computers to monitor these cognitive processes. (JGL)