Educability-and-Group-Differences-1973-by-Arthur-Robert-Jensen

Intelligence and Educability 91
go on increasing steadily throughout the summer months while the
children are not in school, while there is an actual loss in achievement
test scores from the beginning to the end of the summer.
Much of the most recently learned material prior to the summer
vacation has not been sufficiently rehearsed to become consolidated.
The loss is greatest for those school subjects that depend
least upon general intelligence (i.e., the consolidation factor) and
depend most upon sheer learning and memory, such as spelling,
punctuation, grammar, and mechanical or computational arithmetic
and number facts, as contrasted with reading comprehension
and arithmetic concepts (Beggs & Hieronymus, 1968).
Gains in achievement (and intelligence test raw scores) are
relatively greater early in learning than later, largely because it is
easier to consolidate gains at the ‘simple’ end of the scale than at
the more complex (‘difficult’) end of the scale of intellectual tasks.
When students simultaneously begin a new course of study, the
diligent but intellectually mediocre students can keep up or even
excel for a time near the beginning of the course; but soon it
becomes increasingly difficult to keep ahead as they progress
further into the complexities of the subject matter. For the less
intelligent students consolidation does not keep up with their gains
to the same extent as for the brighter students. The growth of
intelligence is not reflected mainly by an increase in the ability for
simple learning through practice, but in the ability to consolidate
and understand increasingly complex material. As Leona Tyler
(1965, pp. 78-9) has put it: ‘The child with an IQ of 80 is handicapped
all through school not because he is slow or inept at learning
things which are within the capacity of all the children at his age
level, but because he is never ready to grasp new and more complex
ideas at the time when they are ordinarily presented to children
of his age.’ Readiness in large part is the ability to consolidate the
knowledge and skills gained through daily learning experiences.
According to our model, at any given point in time, a performance
measure of achievement status (S ) usually reflects more of the
consolidated component (C) than of the gains component (G),
and this is increasingly true over the course of development. Since
C is largely genetic and stable and G is largely environmental and
random, an inference from the model is that brighter siblings (and
twins) should show higher correlations for achievement than duller
siblings. (At any cross-section in time the recent [and random]