My wife's parents did not go to college. Linda's father was a carpenter. Her mother was an aircraft assembly line worker. They grew up in Oklahoma farming families, married, moved to Southern California and raised their children in blue-collar neighborhoods full of families just like theirs.

Linda did go to college, a very selective one. Finding someone like her in that place was unusual. Some of the deans, to her annoyance, reminded her how fortunate she was to have come so far. There are many reasons why Linda became successful academically and professionally. But one did not occur to me until I read a new study about the relationship between books at home and educational attainment around the world.

The study, "Scholarly Culture and Educational Success in 27 Nations," by four researchers in the United States and Australia, is worth reading by those in the Washington area, where the number of books varies so much from family to family, and not necessarily because some parents are well-educated and others aren't. The study, based on 20 years of research, suggests that children who have 500 or more books in the home get, on average, 3.2 years more schooling than children in bookless homes. Even just 20 books makes a difference. The availability of reading material has a strong impact on a child's education, even when controlling for the effects of parental education, father's occupation, gender, nationality, political system and gross national product.

Linda remembers having at least 300 books in her home when she was growing up in the 1950s and 1960s. Many of the books were hers, bought with her $1 weekly allowance and babysitter earnings, often cheaply through the Scholastic Book Club at school. But her father was also a big reader. His collection of Zane Greys and Bret Hartes filled the shelves he built in their home in Lawndale, Calif., with help from Linda's great-uncle John, a cabinetmaker.

Linda's parents purchased the Encyclopedia Americana when she was in intermediate school. They added copies of Reader's Digest condensed books, a favorite of her mother's. Linda devoured those volumes, along with untold numbers of books from her weekly trips to the library.

In other words, like many successful people in this area, she grew up in a book culture established by a family that could not afford many extras but made reading a priority.

The new study led by Mariah Evans of the University of Nevada, Reno, in the journal Research in Social Stratification and Mobility, shows the influence of home libraries on schooling is found nearly everywhere, and it has more power than I expected.

Anyone who has studied the effects of home on learning knows that books are important. The summer learning loss suffered by inner-city children is at least in part the result of them not being encouraged to read, studies suggest. I had associated book reading with affluent parents, because high family income also correlates with school success. But the international study found there was more to it than that.

Even the children of poor, illiterate parents in China, the study shows, on average attained the same academic level as the children of college graduates, if they had opportunities to read. Chinese children who had 500 or more books at home got 6.6 years more schooling than Chinese children without books, the study shows. "Having books in the home has a greater impact on children from the least educated families," it says.

These book habits, as many parents know, never go away. We shampooed the carpets at our house this month, forcing me to move many volumes so the cleaners could get under the bookcases. It nearly killed me, but when Linda and I see books also piling up in the homes of our children, we know it is worth the effort.