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.

A crucial experiment would be to take a large number of very young
children of the lower classes and, after placing them in the most
favorable environment obtainable, to compare their later mental
development with that of children born into the best homes. No extensive
study of this kind has been made, but the writer has tested twenty
orphanage children who, for the most part, had come from very inferior
homes. They had been in a well-conducted orphanage for from two to
several years, and had enjoyed during that time the advantages of an
excellent village school. Nevertheless, all but three tested below
average, ranging from 75 to 90 I Q.

The impotence of school instruction to neutralize individual differences
in native endowment will be evident to any one who follows the school
career of backward children. The children who are seriously retarded in
school are not normal, and cannot be made normal by any refinement of
educational method. As a rule, the longer the inferior child attends
school, the more evident his inferiority becomes. It would hardly be
reasonable, therefore, to expect that a little incidental instruction in
the home would weigh very heavily against these same native differences
in endowment. Cases like the following show conclusively that it does
not:--

X is the son of unusually intelligent and well-educated parents.
The home is everything one would expect of people of scholarly
pursuits and cultivated tastes. But X has always been
irresponsible, troublesome, childish, and queer. He learned to
walk at 2 years, to talk at 3, and has always been delicate and
nervous. When brought for examination he was 8 years old. He had
twice attempted school work, but could accomplish nothing and
was withdrawn. His play-life was not normal, and other children,
younger than himself, abus