The major results and conclusions of a program of research concerned primarily with the relationship of cognitive abilities to learning are summarized. The major purpose of this research was to develop theorems of instruction related to the interaction of task variables and individual difference variables and to develop them in a manner relevant to the instructional designer's task. The studies focused on the relationship of cognitive abilities to the learning of concepts and rules and to the learning of an imaginary science of "Xenograde systems." The goal was to establish a theoretical and methodological continuum from simple concept learning, through the learning of a complex system of concepts and rules, to a set of instructional design procedures which permit transfer of this knowledge into practice. On the basis of the studies a model for research in this area was recommended, cognitive processes relevant for concept and rule learning were defined, and a hypothesis construction model of simple concept learning was outlined, along with proposed theoretical considerations for more complex concept learning and specific recommendations for instructional design utilizing differences in intellectual abilities. (Author)