Crystallized intelligence (Gc) is thought to reflect skills acquired through knowledge and experience and is related to verbal ability, language development^1^ and academic success^2^. Gc, together with fluid intelligence (Gf), are constructs of general intelligence^3^. While Gc involves learning, knowledge and skills, Gf refers to our ability in tests of problem-solving, pattern matching, and reasoning. Although there is evidence that Gf can be improved through memory training in adults^4^, the efficacy of memory training in improving acquired skills, such as Gc and academic attainment, has yet to be established. Furthermore, evidence of transfer effects from gains made in the trained tasks is sparse^5^. Here we demonstrate improvements in Gc and academic attainment using working memory training. Participants in the Training group displayed superior performance in all measures of cognitive assessments post-training compared to the Control group, who received knowledge-based training. While previous studies have indicated that gains in intelligence are due to improvements in test-taking skills^6^, this study demonstrates that it is possible to improve crystallized skills through working memory training. Considering the fundamental importance of Gc in acquiring and using knowledge and its predictive power for a large variety of intellectual tasks, these findings may be highly relevant to improving educational outcomes in those who are struggling
