The testing of 15 year olds done every three years by the Organisation for Economic Co-operation and Development (OECD) Programme for International Student Assessment (PISA) is at the heart of the critique of American education, usually cited as the basis for privatization proposals like replacing lower performing public schools with charters and private school vouchers. If you want to get beyond the cherry picked statistics about “the US is 17th in….etc.,” here is a thoughtful discussion of what it all means with Andreas Schleicher, Head of the Indicators and Analysis Division (Directorate for Education) of the OECD.
A couple of quotes:
“Canada does very well, not just in terms of the average outcomes but in its capacity to moderate socio-economic inequalities, which is a quite big issue in the United States.”
“…a generation ago, the United States was far ahead of everyone. At the age of 15, you would have in the United States more people taking part in education than elsewhere, but this has changed quite a bit, not because the United States got worse, but because progress in schooling has been so much steeper in other countries.”
“…the impact of social background on the success of children is stronger in the United States than in many of the best performing systems….Many of the best performing systems really expect every student to succeed. They set universal, very ambitious standards for all their children. They support their children well. They expect teachers to support their children well. They expect that students learn differently and differently at some times. You can see a high degree of personalized approaches to learning.”
…and lots more, here:
Advancing New Hampshire Public Education 
This OECD study (http://www.epi.org/publication/us-student-performance-testing/) drew the following conclusion regarding PISA: “Because social class inequality is greater in the United States than in any of the countries with which we can reasonably be compared, the relative performance of U.S. adolescents is better than it appears when countries’ national average performance is conventionally compared.” The short response: poverty makes a difference in school performance…
Absolutely.
In the US, students from families in the top economic quintile – the wealthiest 20% – are at the top of all the PISA metrics. We need to find a way to counteract the devastating effects of poverty in America – from prenatal nutrition, health, school attendance, family illiteracy and so on. In the process, we probably have to work on reducing the huge gap between rich families and poor families, bigger in this country than most developed countries in the world.
Fifty years ago racism denied many children a chance for education, and the US made a mighty effort to provide school for ALL our children. Poverty is still a barrier to equal opportunity, and if we want to reach our full potential we need the same kind of commitment to strengthening poor communities and their schools.