The test — known as SERCE and administered by UNESCO — examined the skills of third- and sixth-grade students in 16 Latin American countries. Overall, the results are distressing. Less than 30 percent of the region's third-grade students scored at the top two levels in reading and math; more than 30 percent scored at level one or below in reading—meaning either that they cannot read, or they can read only at the most rudimentary level. Nearly half scored that low in math. Clearly, most of Latin America is doing a poor job of educating its children.

Within the context of generally low scores, Costa Rica, Chile, and Uruguay (which have long had high enrollment rates) did comparatively well. Argentina scored poorly, given its relative wealth. Panama and Peru, despite high rates of economic growth, did relatively poorly. Since UNESCO did not make the test comparable with a similar test it administered a decade ago, we don't know which countries have gotten better or worse. But most striking is that two countries—Cuba and the Dominican Republic—scored much differently than the others. Cuba scored way above the rest of Latin America, while the Dominican Republic scored way below.

In third-grade reading, nearly half of Cuban students scored at the highest level, compared with 1 percent in the Dominican Republic. By contrast, nearly a third of students in the Dominican Republic scored below level one, compared with 1 percent in Cuba.

What is going on? Most Latin American leaders have been reluctant to pay much attention to Cuba's social policy, arguing that because conditions there are so different, its experience offers few useful lessons. There is certainly something to that view. But the presence of such radically different schooling outcomes in two neighboring island countries is worrisome and ought to command our attention. It reminds us that Latin America has a major inequality problem, and raises discomforting questions that need answers. What policies account for Cuba's high levels of achievement? What major, systemic changes will countries like the Dominican Republic have to make in order to raise student learning to adequate levels? International tests of student achievement like SERCE are crucially important in showing us who is doing well and who is not. They sound the alarm. But in order to improve, we need to take the next step and figure out how over- and under-achievers got that way.