Vietnam’s strong performance on the 2012 and 2015 PISA assessments has led to interest in what explains the strong academic performance of Vietnamese students. Analysis of the PISA data has not shed much light on this issue. This paper analyses a much richer data set, the Young Lives data for Ethiopia, India (Andhra Pradesh and Telangana), Peru, and Vietnam, to investigate the reasons for the strong academic performance of 15-year-olds in Vietnam. Differences in observed child and household characteristics explain 37-39 percent of the gap between Vietnam and Ethiopia, while observed school variables explain only about 3-4 additional percentage points (although an important variable, math teachers’ pedagogical skills, is not available for Ethiopia). Differences in observed child and household characteristics explain very little of the gaps between Vietnam and India and between Vietnam and Peru, yet one observed school variable has a large explanatory effect: primary school math teachers’ pedagogical skills. It explains about 10-12 percent of the gap between Vietnam and India, raising the overall explained portion to 14-21 percent of the gap. For Peru, it explains most (65-84 percent) of the gap.