ordinary parent or
teacher does not have. In the case of school children, for example, each
pupil is judged with reference to the average intelligence of the
class. But the teacher has no means of knowing whether the average for
her class is above, equal to, or below that for children in general. Her
standard may be too high, too low, vague, mechanical, or fragmentary.
The same, of course, holds in the case of parents or any one else
attempting to estimate intelligence on the basis of common observation.

THE INTELLIGENCE OF RETARDED CHILDREN USUALLY OVERESTIMATED. One of the
most common errors made by the teacher is to overestimate the
intelligence of the over-age pupil. This is because she fails to take
account of age differences and estimates intelligence on the basis of
the child's school performance in the grade where he happens to be
located. She tends to overlook the fact that quality of school work is
no index of intelligence unless age is taken into account. The question
should be, not, "Is this child doing his school work well?" but rather,
"In what school grade should a child of this age be able to do
satisfactory work?" A high-grade imbecile may do average work in the
first grade, and a high-grade moron average work in the third or fourth
grade, provided only they are sufficiently over-age for the grade in
question.

Our experience in testing children for segregation in special classes
has time and again brought this fallacy of teachers to our attention. We
have often found one or more feeble-minded children in a class after
the teacher had confidently asserted that there was not a single
exceptionally dull child present. In every case where there has been
opportunity to follow the later school progress of such a child the
validity of the intelligence test has been fully confirmed.

The following are typical examples of the neglect of teachers to take
the age factor into account when estimating the intelligence of the
over-age child:--

_A. R. Girl, age 11; in low second grade._ She was able to do
the work of this grade, not well, but passably. The teacher's
judgment as to this child's intelligence was "dull but not
defective." What the teacher overlooked was the fact that she
had judged the child by a 7-year standard, and that, instead of
only being able to do the work of the second grade
indifferently, a child of this age should have been equal to the
work of the fifth