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

Intelligence and Educability 79
processes (Jensen, 1970b). Teaching of the skills before the necessary
maturation has occurred is often practically impossible, but
after the child has reached a certain age successful performance of
the skill occurs without any specific training or practice. The items
in scholastic achievement tests do not show this characteristic.
For successful performance, the subject must have received explicit
instruction in the specific subject matter of the test. The teachability
of scholastic subjects is much more obvious than of the kinds of
materials that constitute most intelligence tests and especially
non-verbal tests.
Still another distinguishable characteristic between intelligence
and achievement tests is the difference between the heritability
values generally found for intelligence and achievement measures.
But this topic is treated in Chapter 4.
GROWTH MODEL OF ACHIEVEMENT
Among the most interesting and theoretically important facts
about scholastic achievement are the manner in which it increases
or ‘grows’ over the years and the particular pattern of intercorrelations
of individual differences in achievement from year to
year over the course of schooling from first grade to high school
graduation. In these aspects, the growth of scholastic knowledge
closely resembles the growth of intelligence, and also, interestingly
enough, it resembles the essential features of growth in physical
stature. Total vocabulary size, one of the best indices of intelligence
that can be measured on an absolute scale, also shows the same
growth characteristics. The evidence relevant to the following
discussion is derived from longitudinal studies in which the
achievements of the same children are measured each year over
the course of their schooling. Much of this evidence has been
compiled by Benjamin Bloom (1964).
In the growth of scholastic knowledge and competence, just as
in the growth of intelligence and of physical stature, individuals
fluctuate in relative standing among their age peers throughout the
course of development. The individual year-to-year fluctuations in
relative standing are greater early in development and gradually
diminish as individuals approach maturity. The year-to-year intercorrelations
of scholastic achievement show a highly distinctive
pattern. I have examined virtually all such longitudinal correlation