Cognitive - achievement relations: findings from a research done in 2010

McGrew and Wendling examined and synthesized studies that looked into the relations between CHC abilities and reading and math achievement.  Their research was published in this paper, available for free download:

CATTELL–HORN–CARROLL COGNITIVE-ACHIEVEMENT RELATIONS: WHAT WE HAVE LEARNED FROM THE PAST 20 YEARS OF RESEARCH. KEVIN S. McGREW AND BARBARA J. WENDLING. Psychology in the Schools, Vol. 47(7), 2010   

The research included 19 studies examining five or more CHC abilities in children.  Because most studies used the Woodcock Johnson (WJ) test, the findings presented here describe mainly the relations between cognitive abilities as measured in the WJ test and achievement as measured in the WJ test.  Most studies were done on the same sample – the national norm sample of the WJ test.

Basic reading skills were measured in this research by single word and non-word decoding, word recognition and linking sounds with symbols.  Reading comprehension was measured by multiple choice and open ended questions about texts and cloze procedures.  Basic math skills were measured by calculation tests ranging from basic math calculations to complex algorithmic computations.  Math reasoning was measured by word problems, number series, and application of math operations and concepts. 

The main findings, in my view (but not all findings) are presented here in an easy to understand visual way.

The results show that sometimes broad abilities are the best predictors, but sometimes narrow abilities are better predictors of achievement.  The results also show that if there is no specific need for an IQ score or a g score, it's not necessary to test the child with the whole intelligence test battery.  It's better to choose the broad and narrow abilities to be tested according to the referral question and to the child's age. 

The authors wonder why visual processing is not a predictor of math or reading achievement.  As for math, past research shows that skills like length estimation are core deficits in math learning disability.  As for reading, the ability to quickly map graphemes to phonemes is known as important for reading.  One possibility is that visual skills related to reading or math are not measured in intelligence tests that measure visual processing.  An argument the goes the other way around would be, that maybe the math tests used in this research don't measure math areas that draw heavily on visual processing (geometry or trigonometry, for example).

I have other questions regarding the fluid ability.  The authors write, that fluid ability tests that predict math achievement best, measure fluid ability through…reasoning with numbers and numerical relations (for example number series or number matrices tests).

Also, fluid ability (as measured by the WJ tests) was not a predictor of reading comprehension (as measured by the WJ tests).  This is odd.  How is it possible, that the ability for abstract reasoning, the ability to draw conclusions and understand consequences is not related to reading comprehension?  One possible explanation is that fluid ability is measured in the WJ test through non-linguistic tests that use visual or numerical stimuli.  It's possible that measuring fluid ability by tests that use verbal stimuli and require verbal abstraction would have helped to find the missing, obvious link between this ability and reading comprehension.