This article analyzes the factors that explain the gap in educational outcomes between the top and bottom quartile of students in different countries, according to their socioeconomic status. To do so, it uses PISA microdata for 10 middle-income and 2 high-income countries, and applies the Oaxaca-Blinder decomposition method. Its results show that students' individual variables only explain differences in high-income countries; meanwhile, school and teacher quality, and better practices, matter even in different institutional settings. From a policy perspective, this evidence supports actions to improve school and teacher quality in order to reduce cross-country differences and differences between students at the top and bottom of socioeconomic distribution. Asia (Indonesia and Thailand), and Latin America (Brazil and Mexico). We also include two high-income countries in Western Europe (the Netherlands and the United Kingdom) to compare the possible differences in students' outcomes between middleand high-income countries-an issue widely considered in the literature since Heyneman and Loxley's (1983) seminal study. Although PISA surveys provide data for many countries, we focus on this small sample of economies because they are representative of areas with divergent societies and educational systems, which scholars have rarely studied from this perspective.
KeywordsWe find that although important differences exist in students' socioeconomic status between high-and middle-income countries, the factors that explain differences in educational outcomes within countries are quite similar. Applying the OaxacaBlinder decomposition method, we suggest that school variables are the most important factor in learning outcomes amongst students of different socioeconomic status.Likewise, variables related to teacher quality are important in most countries, but the effect of these variables is quite small compared to that of school variables.
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ContextMost researchers on the determinants of student outcomes agree that parents' characteristics are the most important predictors of success at school (Coleman et al. 1966;Feinstein and Symons 1999;Haveman and Wolfe 1995). That is, the higher the family's socioeconomic level, the better the student does educationally. However, as we mentioned above, family socioeconomic status affects student performance in different ways. Moreover, it is not the only factor that does so: individual, school, and teacher (2004), report no effect of school type on student outcomes. Likewise, the effect that school size has on student outcomes is unclear. While Barnett, Glass, Snowdon, and Stringer (2002) (2000) and Krueger (2003) found that students perform better in small classes, while Hanushek (2003) and Rivkin, Hanushek, and Kain (2005) did not 4 find the variable had any statistically significant effect on students' educational outcomes. Boarini and Lüdemann (2009) analyzed the impact of school accountability, school autonomy, and spending on the quality of learning. They found evidence ...