In order to deal wisely with human nature in its formative period, the educator must take account of the natural tendencies of human nature to fear, anger, pugnacity, disgust, curiosity, self-assertion and self-display, self-abasement, sex love, sympathy, tenderness, gregariousness, imitativeness, suggestibility, play, jealousy, and other types of behavior. There is no need to decide in the case of each of these traits how much is original and how much is acquired; it is necessary to take account of all of them as persistent motives.

There are certain types of fears which children are prone to develop and definite ways in which the fear motif in their lives can be reduced or directed. There are many types of experience which tend to provoke anger; and in some the anger response is to be encouraged, in others discouraged. If curiosity in the form of natural childish interests is neglected, the result is likely to be the imposition of educational subject matter and procedures which run counter to child nature. Neglect of the deep-seated desire for self-assertion and mastery brings about the formation of inferiority complexes which may paralyze activity or result in over-compensation in the form of conceit,"touchiness," and boastful lying. Neglecting to take account of gregariousness, suggestibility, and imitativeness creates half the problems of school discipline, gives us most of our juvenile delinquents, and renders ineffective some of the best-intentioned efforts of moral education as it is practiced. To ignore the appeal of play and make-believe in the life of children would place us below the most primitive savages in educational wisdom. As for the pervading influence of sex, so much has been written on this subject in recent years that its importance is now generally recognized. It is possible here merely to call attention to some of the X-Y traits which the educational psychologist must take into account; to attempt to formulate desirable educational procedures in connection with each would require a volume.

Individual Differences and Their Causes. One of the most important of the contributions to education which psychology has made is in the field of individual differences. The older psychology was concerned almost entirely with the establishment of general truths concerning human beings; modern psychology is no less interested in the ways in which human beings differ. As soon as attention was focused upon individual differences, it was found that these were omnipresent and very large. It was found, for example, that people differ far more in intellectual ability than they do in height or weight or other physical traits, and that the intellectual differences among school children are a more important factor than pedagogical methods in determining how much a given child will learn. Later, experimentation was begun in the measurement of special abilities and of personality traits, with the result that large individual differences were found wherever a search was made.

One of the leading characteristics of present-day education is the almost universal effort that is being made to shape the work of the school to meet the individual needs of its pupils. Such attempts are affecting not only the pedagogical methods employed, but also goals of instruction, the control of curriculum, and the educational and vocational guidance of children. Special classes are being established for the gifted, the backward, and the predelinquent. Problem children of all types are psychologically studied, and differential treatment is provided not only in the schools but also in the courts and the reformatories. Earlier types of impressionistic case studies are being largely replaced by psychometric techniques which yield quantitative measurements of general intelligence, of special ability in art, music, science, and mathematics, and of such personality traits as ascendency-submission tendencies, inferiority feelings, introversion-extraversion attitudes, mental masculinity and femininity, fairminded-ness, social intelligence, emotional stability, trustworthiness, and occupational and other interests. In all such traits it is found that the range of scores made by unselected children is about as great as it is for intelligence. There is still an immense amount of work to be done in devising new instruments for psychological measurements, improving old ones, and finding the relationships which obtain among various combinations of traits. Nevertheless, the psychology of personality, which only a few years ago seemed too elusive to permit a scientific approach, is rapidly yielding to quantitative treatment. Even temperament and the psychological correlates of physical types are now investigated by scientific methods.

In the use of psychometric techniques it is not necessary to start with any assumption in regard to the cause of the individual differences found. Their purpose is to measure the differences which exist, regardless of how they may have originated. However, when once a satisfactory technique for the measurement of a particular trait has been perfected, it is then possible to investigate the relative contributions of nature and nurture influences. This has been done most extensively in the case of intelligence, but to a less extent also in the case of certain special abilities and personality traits. The existing data pertaining to the relative influence of nature and nuture have been judiciously summarized in Part I of the 1928 Yearbook of The National Society for the Study of Education. The issue is an extremely controversial one, and it is impossible to review here the factual evidence in detail. My own interpretation of the data will be stated in a few brief paragraphs.

In the case of intelligence, as measured by the best intelligence tests, I consider the evidence overwhelming that the larger differences found among children in an unselected school population of a typical American community must be credited to nature rather than to nurture factors. The mere fact that the correlations between parents and offspring and those between siblings are almost always between .40 and .50 in intelligence test scores, of course, proves nothing either way. The correlations can be accounted for on either the nature or the nurture hypothesis. Facts which seem to me to render the nurture hypothesis untenable are the following: