Are cognitive g and academic achievement g one and the
same g? An exploration on the Woodcock–Johnson and Kaufman
tests.
Scott Barry Kaufman, Matthew
R. Reynolds , Xin Liu , Alan S. Kaufman , Kevin S. McGrew Intelligence
(2012)
In a previous post I wrote that IQ scores
correlate 0.4-0.7 with grades in school.
School grade level in influenced by other factors beyond intelligence
(personality factors, quality of instruction, home and school environment etc.).
It turns out that the correlations
between "cognitive g" (general intelligence which is estimated by the
IQ score) and "achievement g" (scores in tests measuring mainly
reading, writing and math that have national norms) – are higher.
Some of the modern intelligence tests
(like the later versions of the Wechsler, Kaufman and Woodcock Johnson) have an
achievement battery in addition to the cognitive battery. The achievement battery measures mainly
reading, writing and math.
The authors of this study assessed the
correlations between children's test scores in the national American sample of
the KABC2 and KTEA2 (Kaufman cognitive and achievement batteries) and between
children's test scores in the national American sample of the WJ3COG and WJ3ACH
(Woodcock Johnson cognitive and achievement batteries).
They found that the average correlation
across ages (4-19) between scores in KABC2 and KTEA2 is 0.86!
The average correlation across ages between
scores in WJ3COG and WJ3ACH is 0.80!
What does it mean?
Intelligence tests are very good
predictors of academic achievement. One of
the leading intelligence scholars in the world, Deary, found that the
correlation between g measured at age 11 and achievement (in national examinations
across 25 different subjects) measured at age 16 was 0.81!
But
the other way around may not be true: in
a research done with special education students, intelligence was predictive of
future achievement whereas achievement
was not predictive of future intelligence. Current achievement may reflect lack
of motivation, lack of opportunity to learn, bad instruction, learning
disability (that lowers achievement but is reflected in only a few low
cognitive abilities).
The high correlation between intelligence
and achievement scores is also a result of mutual influences and interactions
between achievement and cognition: cognitive abilities influence learning, and
the learning process in school improves cognitive processes.
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