Educational psychology mediates between the disciplines of psychology and education. Scholars have seldom agreed on a single definition of the field but have incorporated knowledge from several areas. The discipline of educational psychology was fostered primarily in the United States by such eminent psychologists as William James, Edward L. Thorndike, and James McKeen Cattell. Over the past century, several philosophical and scientific movements influenced the field, the most recent example being cognitive theory. In 1990, the first extensive citation analysis was conducted, illustrating the field's increasing maturity and diversity. Educational psychologists have many opportunities to shape policy during the current period of national educational reform.Educational psychology has come of age. To tell its story requires some arbitrary selection and pointed condensation, as it is a field marked by little definitional consensus, many theoretical persuasions, and diversified scholarship. Published in 1910, the first issue of the Journal of Educational Psychology revealed the field's definitional difficulties. The editors clarified suitable topics for publication as follows:Educational psychology will then be regarded as including not only the well-known field covered by the average text-book-the psychology of sensation, instinct, attention, habit, memory, the technique and economy of learning, the conceptual processes, etc.-but also problems of mental development-heredity, adolescence and the inexhaustible field of child-study-the study of individual differences, of retarded and precocious development, the psychology of the "special class," the nature of mental endowments, the measurement of mental capacity, the psychology of mental tests, the correlation of mental abilities, the psychology of special methods in the several school branches, the important problems of mental hygiene; all these, whether treated from the experimental, the statistical or the literary point of view, are topics and problems which we deem pertinent for consideration in a Journal of Educational Psychology. (Bagley, Seashore, AWhipple, 1910, pp. 1-2) Clearly, there was no overarching, theory of educational psychology in 1910, nor has there ever been.For the past century, however, educational psychology has mediated between the disciplines of psychology and education, and educational psychologists characteristically have applied psychological principles to the practice of education. Glover and Ronning (1987), moreover, identified five broad areas in which educational psychologists have specialized: