The association between school students’ social background and school achievement is well documented. Recent studies demonstrated that this association might be moderated by the level of cognitive potential. Based on these results, we recruited an elementary school sample (N = 837) and an adolescent sample at the end of their compulsory school time (N = 2100) to investigate whether the associations between students’ social background and their academic achievement in math and language arts were moderated by the level of their general cognitive competencies, i.e., intelligence. To this end, we assessed intelligence, math and reading competencies, teacher-reported grades, and students’ socio-economic background (number of books at home). In both samples, the association between students’ socio-economic background and language arts grades was moderated by their intelligence level but not the ones with math grades, reading, and math competencies. The association between socio-economic background and language arts grades was strongest in the average intelligence sample and smaller in the above-average intelligence sample. Results are discussed with regard to their implications for the discussion of social injustice in schools.
