Why are some national systems of education more equitable than others?

Some national systems of education are considered more equitable than others. Equity can be measured along three main dimensions: the strength of the association between students' social origins (socio- economic status, ethnicity, etc.) and educational outcomes, the degree to which educational outcomes vary between schools, and the size of the gap between high- and low-achieving students (i.e., the 'achievement tail'). Previous studies have shown that selective and differentiated educational systems are generally more inequitable than non-selective and comprehensive ones. Nevertheless, some comprehensive systems are less equitable than some selective ones, suggesting that a constellation of social, demographic and educational factors may influence the equity of any given national system of education. This paper uses data from the Programme for International Student Assessment (PISA) to evaluate educational equity in selected OECD member countries. It then attempts to explain national differences in educational equity by examining a variety of social, demographic and educational factors. Based on previous research and theory, it is hypothesized that the most equitable educational systems have non- selective and comprehensive secondary schools that are similarly funded and resourced, and exist in societies that have low levels of poverty and group-based inequality. These factors (among others) are integrated into a matrix so that patterns can be more easily seen and compared