Physiologically and psychologically the child does not function in the same way as the adult, the male not in the same way as the female. Anthropological research offers, therefore, a means of determining what may be expected of children of different ages and this knowledge is of considerable value for regulating educational methods. Anthropological investigations of an age class, let people say of eight-year-old children, show, for a selected social and racial group, a certain distribution of stature, weight, size of head, development of the skeleton, condition of teeth, size of internal organs and so on. Differences in the rate of development may be due to hereditary constitution or to environmental conditions. The rate of development of the individual is expressed primarily by the appearance of definite physiological changes. The same interrelation is expressed in the growth of children belonging to different social classes.