More empirical evidence is needed to answer the question of in what way a family's socioeconomic status (SES) affects student academic achievement, so this study explores the mediating role of cultural capital (CC) in the relationship between SES and student achievement, using the latest approach to testing mediating effects. The data sets from 14 economies in the Programme for International Student Assessment (PISA) 2009 were analysed. In general, the results supported the mediation effects of CC, and the mean of ratios of mediation effects to total effects was 23%. For the three frequently used indices of SES, parents' occupations and education levels had larger impacts on student literacies than did family wealth possession. For most economies, objectified cultural capital (OCC) can explain the effects of all three SES indices on student literacies, but embodied cultural capital (ECC) can only explain the effects of parents' occupations and education levels on student literacies. Whether for reading literacy, science literacy or mathematics literacy, CC theory is applicable in most economies. However, the mediating effects on reading and science literacies were higher than those on mathematics literacy. For different economies, the explanatory power of CC theory was also different.