Discrepancies Between Different Ability Tests - WISC and CogAT tests
By Inderbir Kaur Sandhu, Ph.D
I'm wondering about variations in scores between the CogAT and WISC
tests. We've seen considerable variation, which is confusing!
As a kindergartener, we had our son tested by the school system as we
were trying to figure out what school would serve him best. He tested as
talented and gifted in math, but scored in the 89th percentile on CoGAT
We chose schools poorly, unfortunately, and he started having
significant trouble in 2nd grade. We took him to an educational
consultant. His WISC scores from that time were:
Verbal Comprehension: 155, 99.9th percentile
Perceptual Reasoning: 149,
Working Memory: 104, 61st percentile
112, 79th percentile
Full Scale IQ: 143, 99.8th percentile
We weren't sure if his tester was reliable, since these scores seemed so
high. In third grade his school administered the CoGAT again and he
scored in the 94th percentile.
We went to a different educational/psychological consultant when he was
in 5th grade to confirm a ADHD diagnosis. She gave him the WISC again.
Here are his scores:
Verbal Comprehension: 138, 99th percentile
Perceptual Reasoning: 147,
Working Memory: 99, 47th percentile
118, 88th percentile
General Ability Index: 153, 99.9th percentile
Why would we see such a big difference between scores? This discrepancy
has caught my attention again because his 6-year-old sister was just
tested by the school and she scored in the 91st percentile on the CoGAT.
I'm wondering if we should have her tested with the WISC. The cut off
for talented and gifted services in our district is a 97th percentile
Just a short note on the CogAT. Briefly, it is a measure of a student's
potential to succeed in school-related tasks. It should not be confused
as a measure for intelligence or IQ per se even though it is considered
as an intelligence test. Rather, it measures the reasoning skills that
have developed even though these general cognitive skills are probably
not explicitly taught. They may not be specific to any content area, but
these are skills used in all areas of a student's academic experiences.
Apart from general cognitive skills, the CogAT also measures general
school skills (e.g., ability to listen, follow directions, and focus
attention). It can beneficial when looking for the student's ability to
be successful in school and to look for dominant learning strengths.
Teachers commonly use it when they have concerns over a student's
classroom performance or lack of progress. The scores provide a general
sense of a student's abilities and learning styles, which may lead to
further analysis. Bear in mind that the CogAT is an aptitude test and
measures preparedness for academic work, not the result of instruction
in school. Even though there is a correlation between innate ability and
one's performance, the CogAT is not an IQ test per se.
CogAT is commonly used as screening measures, to see if the child should
move to a full gifted assessment (individual intelligence test). These
tests are commonly administered by teachers and generally normed on
populations of all children, with relatively few gifted children among
the mix. It has been noted that gifted children tend to over-think the
questions when taking group tests and this may cause wrong selections of
options. Furthermore, as there is no individual tester to clarify some
unique (but acceptable) responses, there is a high possibility for
gifted children to often score lower than expected on group intelligence
Tests measure different abilities and have different purposes. Scores on
ability tests may differ due to a few reasons such as the fact that
different tests measures aspects of the same ability; tests are normed
on different group of students and the possibility of errors of
measurement to occur. Therefore, one should not expect that children
must have similar scores on different ability tests. Main reason for the
difference of scores between two ability tests administered to the same
child is due to the somewhat different measures of skills of the same
ability construct. The CogAT measures abstract reasoning abilities in
the three symbol systems most required for learning in school such as
verbal, quantitative, and figural/spatial. Therefore, it has been noted
that CogAT generally predicts school success better than individually
administered ability tests.
I certainly believe that your son is gifted and would require
differentiation in learning. His high scores on VCI and PRI and lower
scores on WMI and PSI is typical for a number of gifted children. Hence
the GAI score is appropriate. For your daughter, perhaps it would be
good to get a standardised IQ test administered. Bear in mind that CogAT
composite score is considered to be most meaningful when the Verbal,
Quantitative, and Nonverbal Battery scores are all at about the same
level (check the breakdown of her scores). If it is not even and
displays unusual scatter, the composite score (and percentile) should
not be regarded as very dependable.
I hope your children will get an ability based educational match. Hope
that helps and wishing you all the best for both your children.