Central to the American dream is the notion that any kid, even one from the poorest of backgrounds, can study hard, do well in school and make it in our society. But many of us fear that the schoolhouse is no longer a path to the middle class. That fear grows with the rising number of U.S. schoolchildren in poverty, and the growing achievement gap in school between them and their wealthier peers.

A recent study examined how much of the achievement gap in math between rich and poor 15-year-old students can be attributed to what material the kids are learning in school, and it found, across 33 countries, that schools are teaching rich kids vastly different math content than poor kids. The researchers calculated that this educational content difference accounts for *a third* of the achievement gap, on average. (The remainder of the achievement gap is explained by socio-economic factors at home, such as family income and parental education.)

“In every society, we want school to be the great equalizer, to help students overcome poverty,” said William H. Schmidt of Michigan State University, the lead author of the study. “In effect, this study says that schooling is making things worse.”

Schooling, or differences in what different children are taught, exacerbates the achievement gap in some countries more than in others. For example, in the Netherlands, schooling accounts for 58 percent of the achievement gap between rich and poor. Korea, Australia and the United Kingdom are also among the “top” nations in which access or exposure to educational content is worsening the achievement gap. In many of these countries, top students, who tend to come from richer families, get steered to elite schools with more rigorous curriculums.

The United States is above the middle of the pack, with 37 percent of the achievement gap between rich and poor explained by differences in curriculum.

Some systems, such as Iceland and Greece, are better at educating poor kids, with less than 20 percent of the rich-poor gap attributable to schooling.

Sweden was the only country studied where schooling wasn’t compounding the achievement gap between rich and poor. There’s still a large achievement gap in Sweden, however, with students in the top quarter of the socioeconomic ladder scoring much higher than students in the bottom quarter.

The study, “The Role of Schooling in Perpetuating Educational Inequality: An International Perspective,” was published on Sept. 30, 2015, in the journal *Educational Researcher*. Two other researchers from Michigan State also collaborated on it, along with Pablo Zoido of the Organization for Economic Co-operation and Development (OECD).

Because of additional student survey questions on the 2012 international tests known as PISA, the researchers were able to learn exactly which math topics students said they had covered in school. Students who had studied more topics, such as quadratic or linear equations, tended to score higher on the PISA math test. And there was also a strong correlation between a student’s socioeconomic status and whether he or she had studied a math topic frequently in school. Using statistical techniques, the researchers teased out exactly how much of the rich-poor gap was due to socioeconomic status at home, and how much was coming from school.

I asked Schmidt if his study is a condemnation of tracking, where bright students are steered into more advanced classes or schools. He said his study doesn’t definitively prove that tracking is the mechanism that is exacerbating the rich-poor divide in schools. “But it’s certainly a big part of it,” he said. “It calls into question any sorting of students.”

He argues that all students should be taught the same topics, and that more advanced students should be given opportunities to go deeper with the material, instead of racing ahead to calculus. One thing worth noting is that the PISA math test covers the application of rather basic math concepts, such as calculating percentages and solving simple algebra equations. Not even advanced algebra is needed to do well on the exam. And yet, higher-income students report having covered the basic mathematical concepts more frequently, and they succeeded more in applying these math concepts on the test.

Interestingly, tracking works differently in the U.S. than in other countries, where rich kids are steered to different schools rather than different classrooms. “In France, Germany and Japan, the inequalities are larger between schools,” Schmidt explained. “But in the U.S. there are greater content inequalities inside the schools.”

In other words, richer kids get steered to more rigorous math classes and poorer kids get steered to watered-down math classes. This is often happening in eighth grade, when some students are tracked into algebra and some aren’t. But Schmidt says there are even vast content differences in sixth- and seventh-grade classrooms in the same school.

“Everyone talks about failing schools. But the policy implication here is that we should stop focusing on failing schools. The bigger piece is something within,” said Schmidt.

Even the best schools in the U.S. need to look carefully at how they are sorting students, and whether they are reinforcing the gap between rich and poor, rather than reducing it.