It has in fact been found wherever comparisons have been made that children of superior social status yield a higher average mental age than children of the laboring classes. The results of Decroly and Degand and of Meumann, Stern, and Binet himself may be referred to in this connection. In the case of the Stanford investigation, also, it was found that when the unselected school children were grouped in three classes according to social status (superior, average, and inferior), the average I Q for the superior social group was 107, and that of the inferior social group 93. This is equivalent to a difference of one year in mental age with 7-year-olds, and to a difference of two years with 14-year-olds. However, the common opinion that the child from a cultured home does better in tests solely by reason of his superior home advantages is an entirely gratuitous assumption. Practically all of the investigations which have been made of the influence of nature and nurture on mental performance agree in attributing far more to original endowment than to environments. Common observation would itself suggest that the social class to which the family belongs depends less on chance than on the parents' native qualities of intellect and character. The results of five separate and distinct lines of inquiry based on the Stanford data agree in supporting the conclusion that the children of successful and cultured parents test higher than children from wretched and ignorant homes for the simple reason that their heredity is better. The results of this investigation are set forth in full elsewhere.[42] [42] See _The Stanford Revision and Extension of the Binet-Simon Measuring Scale of Intelligence_. (Warwick and York, 1916) It would, of course, be going too far to deny all possibility of environmental conditions affecting the result of an intelligence test. Certainly no one would expect that a child reared in a cage and denied all intercourse with other human beings could by any system of mental measurement test up to the level of normal children. There is, however, no reason to believe that _ordinary_ differences in social environment (apart from heredity), differences such as those obtaining among unselected children attending approximately the same general type of school in a civilized community, affects to any great extent the validity of the scale.