The effects of variation in instructional media design for all learners and for low and high ability learners considered separately are investigated in this paper, and the results are collected into a set of prescriptions for instructional media design. The literature of the aptitude-treatment interaction field is reviewed, and 10 statements on learning are made which are considered generally supported by the research. These are collected into separate lists of factors or variables that disproportionately benefit either high mental ability students or low mental ability students. Those instructional procedures that benefit low ability learners are characterized as largely serving a "compensatory" function, that is, they provide the mediators, organization, and modality that the students cannot provide for themselves. In turn, the instructional procedures that benefit high ability students serve a "preferential" function by calling on and utilizing their higher aptitudes. These generalizations are then expanded to form very detailed prescriptions for instructional media design, depending on the mental ability of the learners. (WH)