The children included in the Investigation were 479 boys and 476 girls of approximately nine years of age and 346 boys and 337 girls of approximately thirteen years of age. Irregularity of attendance caused retardation in school especially in the case of boys, and was most marked among professional workers' children and children from overcrowded houses. Owing to this irregularity a child's position in school could not be taken alone as an index of its mental capacity. Children from smaller sized or overcrowded houses, largely inhabited by manual workers, were frequently dirty and poorly clad, and were in marked excess in the retarded divisions, while children who were clean and had good clothing preponderated in the advanced division. The retardation might be negatived to a certain extent by the earlier age of entry to school of children of this type. The active factor appeared to be the poorer nutrition. There was a larger percentage of manual workers' children in the lower mental capacity divisions, while an increased proportion of children of sedentary workers were advanced pupils and the children of professional men clustered round the normal and retarded divisions. There was a marked tendency for girls to find their way into relatively more advanced classes than boys. There was a steady decline in nutrition with descending mental capacity, except in the XIII. years group advanced division, where the girls were not increased in height and weight over their fellows. Children of sedentary workers were taller and heavier than children of manual workers but smaller and lighter than those of professional workers, i.e., height and weight figures varied according to the number of apartments in the home, or, more exactly the degree of overcrowding. Irregular attenders, children with physical defect, and children employed out of school hours, were as well nourished as their fellows. Maternal efficiency, income per person, nutrition of the child, and milk consumption varied directly with each other and inversely with overcrowding. The proportion of income spent in rent and taxes varied directly with maternal efficiency and nutrition but inversely with overcrowding and income per person. Maternal efficiency appeared to be more closely allied to the physical and hence the mental welfare of the children than any of the other factors investigated. Physical defect was more marked in manual than in sedentary and in sedentary than in professional workers' children. While one physical defect as a rule was insufficient to cause retardation, the combined action of several might do so. Children suffering from defective vision (uncorrected) were retarded in school. Enlargement of tonsils and anaemia or functional cardiac defect apparently did not affect the position in school. It did not appear that transferring children from slum areas to good housing conditions did in itself improve their physical development. Employment out of school hours did not cause retardation, though it reduced the numbers of hours in bed per night. With regular attenders, grouping according to mental capacity was the same as grouping according to intelligence. These general results cannot be applied to individual cases
