The current study reports on an intervention study that investigated the relative contributions of 5-week English language training (ELT) and 5-week working memory training (WMT) to improvements in English language knowledge and working memory capacity in university learners of English as a foreign language. The participants were allocated to one of the following three experimental groups and a control group: (i) ELT only; (ii) WMT only; and (iii) both WMT and ELT. The results showed that intervention effects were pronounced in the WMT + ELT group, who improved scores on the reading span test and all tests of verbal and visuo-spatial short-term and working memory. The gains on verbal short-term (Japanese) and working memory (Japanese and English) were maintained 3 months later. None of the interventions, single or combined, were associated with gains in foreign language knowledge, however. The sustained effects of the dual approach and its implications are discussed.