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

The Heritability of Scholastic Achievement 107
School differences and teacher differences are more strongly
reflected in those school subjects which are least apt to be taught
or practised at home under parental supervision. Parents probably
pay more attention to their children’s reading and have more
influence over it than any other subject, and therefore there should
be relatively smaller sibling differences in reading skills. When
parents pay little attention to children’s scholastic progress, the
environmental component of sibling differences is a function of
teacher differences and, if siblings have different teachers or attend
different schools with somewhat different curricula, there will be
little or no sibling correlation between the specific environmental
influences on their learning of school subjects.
Still another factor affecting the h2 of achievement is the degree
of correspondence between the school’s curriculum and the subject
content of the achievement tests. There is sometimes very poor
correspondence between what is actually taught in class and what
is assessed by the standardized achievement tests. Such discrepancies
can either attenuate estimates of h2 for scholastic achievement,
or can leave the outcome ambiguous by causing the achievement
test to become a measure of incidental learning in and out of
school, rather than intentional learning in the classroom, thereby
resembling more a general intelligence test. One of the characteristics
of the more intelligent children is that they are better
incidental learners; they somehow pick up and retain much more
information than is directly taught to them or than they learn
intentionally.
Thus, unlike the heritability of intelligence, the heritability of
scholastic achievement as it is usually estimated is so conditional
upon a large variety of other variables as to be a rather unstable
datum.
FAMILY INFLUENCES ON SCHOLASTIC ACHIEVEMENT
One reflection of the relative environmental influences of the family
and of the school on children’s scholastic achievement is the
magnitude of the intraclass correlation among full siblings. The
total variance in test scores, cr2, is analyzable into two main
components: (a) variance between families,1 and (b) variance
within families (c 2,). Thus, a2 = Og + c 2,. The intraclass correlation,
rf, among siblings is2