The tests of musical ability help to identify, even in the lower school grades, the children who have musical promise. In the past, millions of dollars have been expended annually on the musical education of children who were almost wholly lacking in musical talent, while countless others of superior natural talent remained undiscovered. The same is true with respect to artistic talent, mechanical aptitude, and other types of special ability. The rapid progress which is being made in psychological testing warrants the belief that in the not very distant future the vast majority of school children will be measured for several kinds of special ability and special defects as well as for general intelligence and for previous scholastic achievement.

The personality tests will doubtless have less effect on ordinary classroom procedures, but their ultimate influence upon child training in the broader sense is likely to be profound. It is already apparent that the early treatment of children by parents is capable of warping their personality traits for life in definitely measurable ways. Lack of opportunity for self-expression breeds inferiority complexes that interfere with normal personality development. Lack of normal social contacts, especially if this is combined with a sense of inferiority, leads to extreme introversion. Too much mothering of the boy or too much fathering of the girl warps the child in the direction of homosexuality. Attitudes of honesty, fair-mindedness, and tolerance in home and school definitely affect the scores which children make on tests of these traits. Such influences have long been suspected; they are now being quantitatively measured. In the case of honesty and trustworthiness, for example, it has been experimentally demonstrated that the child is much less influenced by what he is taught verbally than he is by the general atmosphere of honesty and truthfulness in the classroom or home.

The measurement of interests is especially promising as an aid to vocational guidance. It has been shown that the child himself cannot be depended upon to give a correct account of his interests. He easily misjudges his interest in a given school subject because of his attitude toward the teacher; he misjudges his interest in a given occupation because of his admiration for some one in that occupation. In fact the child has no possible means of knowing whether his interests and attitudes most resemble those of lawyers, doctors, engineers, artists, teachers, business managers, or some other occupational group; but interest tests have been devised to answer just this question. They cannot serve as the sole basis of vocational guidance, but they promise to become indispensable aids.

The above are only examples of many illustrations that could be given to show how the study of individual differences is influencing education. In the mass education so necessary in a democracy, individuality has always been sacrificed in greater or less degree in favor of a uniform product. But a democracy, to survive and progress, demands not only a high level of general attainment in its population, but leadership as well. Psychological measurements of the kind we have described are making it possible to identify exceptional talent of every kind and to rescue the individual from the mass. Many problems remain to be solved before this end can be accomplished, but substantial progress is being made.

Mental Development. Since the beginning of the child study movement in the eighties of the last century, innumerable researches have been published in the psychology of mental development. These have included psycho-biological studies of various life periods, especially of early infancy and adolescence, studies of language development, growth in character and personality traits, and age changes in general intelligence, special abilities, and interests. The amount of such research is constantly increasing, and its character is becoming more scientific. The child-study enthusiast of forty years ago was usually ill trained in scientific method, and his results were of little or no value. At present there are in the public schools, in institutes for child welfare research, in child guidance clinics, in juvenile courts, and in institutions for defectives and delinquents hundreds of well-trained psychologists investigating the problems of mental development. It is possible here only to indicate the types of problems which are being studied and to state briefly a few of the more important conclusions to which investigators have been led.

The rate of mental growth was formerly thought to be irregular and to give the effect of well-defined stages. It has been found, on the other hand, that development is gradual and regular, almost totally lacking in saltatory character. Early childhood is not preeminently a sensory stage, middle childhood a motor activity stage, pre-adolescence a memorizing stage, and adolescence a stage of rapid intellectual growth. It is true that any two periods, separated by a few years, present fairly clear differences, but new capacities rarely, if ever, develop suddenly. Generally speaking, mental growth proceeds at a gradually decreasing rate from infancy to maturity. It is greatest in the first year, somewhat less in the second year, still less in the third, and so on, until by the age of fifteen or sixteen the changes from year to year have become relatively small. It is possible that interests and attitudes are subject to more sudden changes than are intellectual abilities, but for the most part they too run an even course. Even the rebirth which adolescence is popularly supposed to bring is largely a myth. Still less is there ground for believing, as Stanley Hall did, that the child in the period from eight to twelve years is especially adept at memorizing and incapable of any genuine reasoning, or that he lacks appreciation of moral values and responds only to authority. Sweeping and untrue or half-true generalizations of this kind have done much harm, especially in justifying radical shifts in educational procedures from grade to grade. Until very recently, for example, kindergarten methods used with five-year-olds differed so completely from the methods used with six-year-olds in the first-grade that one would have supposed children of these two ages could have hardly any traits in common. One of the most important aspects of educational progress in the last quarter century is that concerned with the integration of lower and higher school grades all along the line to conform with the natural development of the child. This growing recognition of law governing mental development has caused the psychologist to turn his attention to the possibilities of prediction. Formerly the parents of a defective child were encouraged to hope that the child would outgrow his backwardness, and that, in general, a child's present abilities and behavior tendencies have little significance for later development.