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The percentage 7.5 compares with 8 found to be certifiably defective in last
year's Ponton-road series of 401 cases, and with Professor Burt's estimate of 8.
Of the 51 certifiable cases, 34 were known to be defective prior to admission
to Ponton-road ; 17 hitherto unsuspected defectives were discovered as the result of
examination there.
Tables C, D, E, F and G give summaries of the result of the examinations. For
educational levels, Professor Burt's standardized reading and calculation tests were
used ; the Stanford revision of Binet's scale and Healy's form boards were used to
estimate mental ages. In addition, a careful Porteus Maze test was made in 668
cases. The Porteus Maze test was selected as a test of intelligence as expressed
in the form of practical ability as distinct from intelligence, which requires for its
expression the use of verbal imagery. It is a valuable test in that it is accurately
standardized, is independent of scholastic attainments and is a useful indicator in
forming an estimate of the co-ordination between hand and eye, and thus to some
degree of the level of attainment and the potential level of the subject in practical
work. In addition, it brings to light the presence or absence of certain emotional
qualities, such as impulsiveness, caution, foresight, patience, etc.

Although 51 certifiable defectives are included in the 695 cases examined, it
is evident that serious mental retardation is present in the majority. Eliminating
the 26.2 per cent. who test up to their chronological ages, and taking out also the
7.5 per cent. known defectives, there remain about 65 per cent. of the whole group
who are backward—many of them not far above the borderline of mental defect.
Table D.—695 cases, as before, were examined as regards their educational, reading
and calculation attainments. In making this table the mean of the reading and
arithmetic ages, estimated on Prof. Burt's scale, is taken to indicate the general
educational level. Thus a child who reads up to the 11-year level and whose level
for calculation is 7, is given an educational age of 9. In actual fact, the levels for
arithmetic are invariably much lower than those for reading in this series.

As above, discounting the 10.5 per cent. testing up to their normal level and
the 7.5 per cent. known defectives, there remain 72 per cent. showing educational
backwardness—extreme backwardness in many cases. It is clear from scrutiny of
Tables C and D that this educational backwardness is not altogether due to lack of
intelligence, but that there is here, also, a considerable failure in achievement, that
is to say, a large percentage fail educationally to reach even their mental ages,
that is, they fail to do as well as they are capable of doing.
Table E.—Shows the results in 668 cases examined by the Porteus Maze test.
The backwardness brought out by this practical test is even more striking than that
shown in Tables C and D. Only 8.8 per cent. test up to their chronological ages.
Eliminating these and the 7.5 per cent. known defectives, there remains the enormous
figure of 83 per cent. showing backwardness in a test requiring practical ability, and
G