There is today ample evidence that academic achievement depends on individual disparities in socioeconomic status (SES), working memory (WM) and academic self-concept (ASC). However, because these factors were investigated intensively but in separate fields of research in the past four to six decades, their relationships remain largely unknown. The present study investigated whether SES, WM and ASC interact with each other or represent independent contributions to academic achievement in 2379 adolescents in middle and high schools. The findings confirmed previous results showing that students with lower SES, lower WM and lower ASC perform less well on academic tests. Above all, they revealed subtle patterns of mediating processes. Specifically, individual differences in WM processing, and to a lesser extent in ASC, accounted for most part of the negative impact of low SES on academic achievement. These findings indicate that being a member of disadvantaged groups impair both WM processing and ASC and provide a clearer picture of the complex involvements of socioeconomic, cognitive and self-perception factors in academic achievement.