Richard Wilkinson and Kate Pickett (2010) have published a book in which they claim that in more equal societies people on average have better health, higher education, higher social mobility and there is less stress, drug consumption and violence. The authors are convinced that economic inequality affects peoples’ intellectual abilities (Wilkinson and Pickett, 2007). Richard Lynn and Tatu Vanhanen (2006) have shown the same relationship based on a sample of 146 countries. The GINI index of inequality of income had a correlation of -0.34 with literacy in the sample countries, a correlation of -0.42 with gross national income, a correlation of -0.45 with life expectancy, etc. Big differences in income reduce human development, and therefore, people seek ways to reduce inequality (Asghar, Awan and Rehman, 2011).

Economics and education are tightly related to each other. For example, Lynn et al. (2007, 867) have found a correlation of 0.66 between TIMSS and PISA test results in 67 countries and the logarithm for gross domestic product (GDP). Due to the tight relationship between education and economics, it can be assumed that large differences in education reduce average achievement in countries. This assumption is supported by the overall desire to maximise equity in education, for example, through the equal distribution of resources (Gamboa and Waltenberg, 2012), raising the average level of education (Keller, 2010), etc.   

Studies about the role of variance in achievement have primarily been conducted within countries, and have shown contradictory results at class level. Some studies have shown the advantage of grouping students into homogeneous groups; other studies have not found the same effect (Scharenberg, 2012).

The aim of the research below is to study the relationship between the variance of PISA results on the one hand and PISA scores and economic development of countries on the other. The analysis will be conducted on the basis of student and school level data. The hypothesis is that large differences between students and schools are related to lower PISA scores and lower GDP.

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