This is particularly the case in societies with high levels of inequality, where the probability of tertiary educational attainment of children in lower-income groups is significantly lower than that of children in other income groups (Figure 2) (OECD, 2015b). The level of education of parents (high, medium and low) is used in this figure as a proxy for socioeconomic status. Low PEB: neither parent has attained upper secondary education, medium PEB: at least one parent has attained secondary and post-secondary, non-tertiary education, high PEB: at least one parent has attained tertiary education.