To achieve maximum utility, the development of knowledge or skill passes through four distinct phases of learning: acquisition, fluency building, application, and adaptation. Some have defined each phase of learning solely in terms of behavioral outcome (e.g., acquisition leads to the achievement of accuracy and consistency in the recall of knowledge or the demonstration of a skill), but each phase of learning has somewhat different implications for effective instruction, and it is on the basis of those implications that the various phases of learning have been most thoroughly studied and defined.