Instructional clarity is a cluster of instructor behaviors that contains an appropriate use of keys, links, framing statements, focusing, and examples and avoids vagueness terms and mazes. In this study, students' (N=59) achievement and their perception of clear instruction were significantly affected by both the amount of clarity an instructor provided in a classroom presentation and the type of conceptual structuring that was used in a lesson's design. The number of keys, links, framing, focusing, and example moves made by an instructor predicted the amount of achievement that a student would be able to attain in defining, identifying, and applying concepts. Students who were presented with lessons containing more positive instructional clarity moves achieved more. Clear instruction is most beneficial when a variable coordinate concept structure is appropriately used. Achievement of college students is negatively affected by unclear presentations of even well-structured, conceptually presented material. As a concept structure becomes less complex, the amount of instructional clarity becomes less relevant. (IAH)