This article began by suggesting that different processes are likely to mediate alterations in behavior and cognitive structure and that conditioning principles do not seem sufficient to explain all the classes of change. Although the acquisition of conditioned responses, the potentiation of inborn capacities, and the establishment of schemata probably implicate different processes, all three involve selective attention to sensory events, whether these events function as conditioned stimuli, releasers of innate response dispositions, or the bases for mental representations. Hence, better understanding of the forces that control selectivity and duration of attention should provide insights into the nature of psychological growth, especially the lawful alterations in cognitive structure that seem to occur continually as a function of the child's encounter with discrepant events. The heart of this article was devoted to this theme. It was argued that events that possessed a high rate of change in their physical characteristics, that were moderately discrepant from established schemata, and that activated hypotheses in the service of assimilation had the greatest power to recruit and maintain attention in the young child.