 Needless to say, I am especially pleased by the central place of prior knowledge in the studies appearing in this issue. It was nice to see research support for the argument made over many years (Tobias 1973, 1976, 1989, 2003, 2005) that prior knowledge plays a central role in such research. Specifically, the general hypothesis guiding prior ATI studies of interactions between prior knowledge and instructional methods was that students with low prior knowledge needed substantial instructional support to learn effectively, whereas those with high prior knowledge could succeed with limited support [see Tobias (2009) for extended discussions of both instructional support and the advantages of seeking ATIs involving prior knowledge that are beyond the scope of this paper; recommended research designs for ATI studies can be found in Tobias (in press)]. Each of the studies in this issue offers consistent backing for the ATI between prior knowledge and instructional support, whether the support consists of adding iconic representations, metacognitive prompts, guided instruction, adaptive computer tutors, or segregating content to make the material more comprehensible.