The data are unequivocal: kids from wealthy families do better in school than kids from poor families. It's observable across ages, on all sorts of different measures, and (to varying degrees) in every country.

A piece I wrote for the American Educator on this phenomenon is just out. You can read it here. A very brief summary follows.

A great deal of research from the last ten years can be summarized in two broad theories.

Family Investment theories offer the intuitive idea that wealthier parents has more resources to invest in their kids, and kids, naturally enough, benefit. Financial resources can go to enrichment experiences in the summer, more books in the home, a tutor if one is needed, better access to health care, and so one.

Wealthier parents are also likely to be higher in human capital--that is, they know more stuff. Wealthier parents speak more often to their children, and with a richer vocabulary, with more complex syntax, and in a way that elicits ideas from the child. Wealthier parents are also more likely to read to their children and to buy toys that teach letters and the names of shapes and colors.

Finally, wealthier parents are more likely to be rich in social capital--that is, they are socially connected to other people how have financial, human, or social capital.

The second family of theories on this phenomenon is Stress theory.  Stress theories apply particularly to low-income families, and suggest that poverty leads to systemic stress--stress caused by crowding, by crime-ridden neighborhoods, by food uncertainty, and other factors. This stress, in turn, leads to emotional problems in parents, which leads to ineffective parenting strategies. Stress also leads directly to brain changes in children. Both of these factors lead to emotional and cognitive disadvantage for kids.  The theory is summarized in the figure.

The article elaborates on these theories in more detail and I provide citations there.

I close with this paragraph:

The research literature on the impact of socio economic status on children's learning is sobering, and it's easy to see why an individual teacher might feel helpless in the face of these effects. Teachers should not be alone in confronting the impact of poverty on children's learning. One hopes that the advances in our understanding the terrible consequences of poverty for the mind and brain will spur policymakers to serious action. but still, teachers should not despair. All children can learn, whatever their backgrounds, and whatever challenges they face.

An article in yesterday’s New York Times covered some recent research on the increasing education achievement gap between rich and poor. It’s worth a read, but it misses a couple of important points.      

     Regarding reasons for the gap, the article dwells on one hypothesis, commonly called the investment theory: richer families have more money to invest in their kids. (The article might have mentioned that richer families not only have more financial capital, but more human capital and social capital.) The article does not mention at all another major theory of the economics of educational achievement; stress theory. Kids (and parents) who live in poverty live under systemic stress. A great deal of research in the last ten years has shown that this stress has direct cognitive consequences for kids, and also affects how parents treat their kids. (Any parent knows that you’re not at your best when you’re stressed.) An open-access review article on this research can be found here.

      Another important point the article misses concerns what might be done. It ends with a gloomy quote from an expert: “No one has the slightest idea what will work. The cupboard is bare.”

     I think there is more reason for optimism, because other countries are doing a better job with this problem than we are. The OECD analyzes the PISA results by reported family SES. In virtually every country, high SES kids outperform low SES kids. But in some countries, the gap is smaller, and that’s it’s not just countries that have smaller income gaps.

      Economic inequality within a country is often measured with a statistic called the Gini coefficient which varies from 0 (everyone has the same net worth) to 1 (one person has all the money, and the other has nothing). Rich children score better than poor children in countries with large Gini coefficients (like the US) and the rich outscore the poor in countries with lower Gini coefficients (like Norway). Being poor predicts lower scores everywhere, but the disparity of wealth means more in the US than it does in other countries. What’s significant is that the relationship between income and test performance is stronger in the US than it is in most countries. (The US has the 3rd strongest relationship between income and student performance in Science and 10th highest for math, in the 2006 PISA results).

         Some countries, (e.g., Hong Kong), despite an enormous disparity between rich and poor, manage to even the playing field when the kids are at school. The US does a particularly poor job at this task; wealthy kids enjoy a huge advantage over poor kids. People generally argue that the US is different than Hong Kong, we’re a large, heteroogenous country, and so forth. All true, but the defeatist attitude won’t get us anywhere. We need more systematic study of how those countries solve the problem.