ildren of the superior social class is
about 7 points above, and that of the inferior social class
about 7 points below, the median I Q of the average social
group. This means that by the age of 14 inferior class children
are about one year below, and superior class children one year
above, the median mental age for all classes taken together.

2. That the children of the superior social classes make a
better showing in the tests is probably due, for the most part,
to a superiority in original endowment. This conclusion is
supported by five supplementary lines of evidence: (a) the
teachers' rankings of the children according to intelligence;
(b) the age-grade progress of the children; (c) the quality
of the school work; (d) the comparison of older and younger
children as regards the influence of social environment; and
(e) the study of individual cases of bright and dull children
in the same family.

3. In order to facilitate comparison, it is advisable to express
the intelligence of children of all social classes in terms of
the same objective scale of intelligence. This scale should be
based on the median for all classes taken together.

4. As regards their responses to individual tests, our children
of a given social class were not distinguishable from children
of the same intelligence in any other social class.

THE RELATION OF THE I Q TO THE QUALITY OF THE CHILD'S SCHOOL WORK. The
school work of 504 children was graded by the teachers on a scale of
five grades: _very inferior_, _inferior_, _average_, _superior_, and
_very superior_. When this grouping was compared with that made on the
basis of I Q, fairly close agreement was found. However, in about one
case out of ten there was rather serious disagreement; a child, for
example, would be rated as doing _average_ school work when his I Q
would place him in the _very inferior_ intelligence group.

When the data were searched for explanations of such disagreements it
was found that most of them were plainly due to the failure of teachers
to take into account the age of the child when grading the quality of
his school work.[26] When allowance was made for this tendency there
were no disagreements which justified any serious suspicion as to the
accuracy of the intelligence scale. Minor disagreements may, of course,
be disregarded, since the quality of school work depends in par