Normally, the LAP contains a list of activities. Although there is some selection, the choice involves mostly the amount of material and/or supplementary material. The implication of this practice is that the only characteristic of aptitude is the time factor as postulated by Carroll. However, previously cited references to the difference in cognitive style and the affective-social domain indicate that such an assumption is not justified on the basis of available evidence. (See chapter 4, "Research," pages 68-77.) In fact, as early as 1957, Cronbach, in his American Psychological Association (APA) presidential address, urged educational researchers to "design treatments not to fit the average person, but to fit groups of students with particular aptitude patterns" and to "seek out aptitudes that correspond to modifiable aspects of the treatment." He believed that "treatments should be differentiated in such a way as to maximize their interaction with aptitude variables" (Boutwell & Barton, 1974, p. 13). Research goals have shifted from the illusive dream of the one best method to the best method for the particular student. Much recent research has dealt with aptitude-treatment interactions in an attempt to ascertain which students learn best by which methods. (See chapter 4, "Research," pages 91-92.)
Another aspect of Carroll's postulate is that given enough time most learners can learn most material. Carroll assumes that the learner either has (or will be given) the necessary prerequisite skills to complete the given learning task. Currently, most neobehaviorists and cognitive psychologists support a hierarchical model of learning. Gagne's (1965) model contains eight types of learning, each more complex than the preceding and each depending upon the preceding. Piaget conceives of the development of cognitive skills as occurring in five stages, each growing out of and being at a higher level of complexity and abstraction than the previous (Gorman, 1972). If hierarchical models are appropriate, the assumption must be made that in order to learn anything the learner must know, or be taught, all the necessary prerequisite knowledge and skills in order to complete the designated learning task itself. In some cases this necessity would lead to a point of diminishing returns, although the accomplishment of such a procedure is theoretically possible. Even this theoretical possibility is rather slight in some contexts since one can easily postulate that the individuals' inherent intellectual capacities place some limit upon the heights of abstraction, conceptual thought, and symbolic processes to which they can attain.