Summary: Why does the United States lag behind so many other countries on international education assessments? The traditional view targets school-based explanations—U.S. schools attract poorer teachers and lack the proper incentives. But the U.S. educational system may also serve children with comparatively greater academic challenges as a result of poorer social conditions. One way of gaining leverage on this issue is to understand when U.S. students fall behind their international counterparts. I first compare reading/ vocabulary test scores for U.S. and Canadian children (ages 4-5) using National Longitudinal Study of Youth 1979–Children and Youth (NLSY79) and Canada’s National Longitudinal Study of Children and Youth (NLSCY). I then compare the magnitude of these differences to similar cohorts of students at ages 15 to 16 using data from the Programme for International Student Assessment (PISA). Findings indicate that while the Canadian advantage in PISA is substantial (0.30 standard deviation units), this advantage already existed at ages 4 to 5, before formal schooling had a chance to matter. I discuss the implications of this pattern for interpreting international test score rankings.
