freakonomics

measure children with a lot of books against children with no books, the answer may not
be very meaningful. Perhaps the number of books in a child’s home merely indicates how
much money his parents make. What we really want to do is measure two children who
are alike in every way except one—in this case, the number of books in his home—and
see if that one factor makes a difference in his school performance.
It should be said that regression analysis is more art than science. (In this regard, it has a
great deal in common with parenting itself.) But a skilled practitioner can use it to tell
how meaningful a correlation is—and maybe even tell whether that correlation does
indicate a causal relationship.
So what does an analysis of the ECLS data tell us about school-children’s performance?
A number of things. The first one concerns the black-white test score gap.
It has long been observed that black children, even before they set foot in a classroom,
underperform their white counterparts. Moreover, black children didn’t measure up even
when controlling for a wide array of variables. (To control for a variable is essentially to
eliminate its influence, much as one golfer uses a handicap against another. In the case of
an academic study such as the ECLS, a researcher might control for any number of
disadvantages that one student might carry when measured against the average student.)
But this new data set tells a different story. After controlling for just a few variables—
including the income and education level of the child’s parents and the mother’s age at
the birth of her first child—the gap between black and white children is virtually
eliminated at the time the children enter school.
This is an encouraging finding on two fronts. It means that young black children have
continued to make gains relative to their white counterparts. It also means that whatever
gap remains can be linked to a handful of readily identifiable factors. The data reveal that
black children who perform poorly in school do so not because they are black but
because they tend to come from low-income, low-education households. A typical black
child and white child from the same socioeconomic background, however, have the same
abilities in math and reading upon entering kindergarden.
Great news, right? Well, not so fast. First of all, because the average black child is more
likely to come from a low-income, low-education household, the gap is very real: on
average, black children still are scoring worse. Worse yet, even when the parents’ income
and education are controlled for, the black-white gap reappears within just two years of a
child’s entering school. By the end of first grade, a black child is underperforming a
statistically equivalent white child. And the gap steadily grows over the second and third
grades.
Why does this happen? That’s a hard, complicated question. But one answer may lie in
the fact that the school attended by the typical black child is not the same school attended
by the typical white child, and the typical black child goes to a school that is
simply…bad. Even fifty years after Brown v. Board, many American schools are
virtually segregated. The ECLS project surveyed roughly one thousand schools, taking