This article is one of the first attempts to study the mechanisms of foreign language learning by children with DLD. We test the effectiveness of a cognate intervention aiming to enhance cross-linguistic awareness of Dutch-speaking primary-school pupils with DLD, as part of their English as a Foreign Language (EFL) curriculum. The participants were learning English as a school subject in the last three years of special primary education in the Netherlands (ages 8;11-13;8). The intervention group (n = 41) received 12 short lessons on cognate relationships over the course of 14 weeks. The control group (n = 46), matched to the intervention group on the amount and intensity of foreign language instruction, received their regular English lessons that were mainly implicit and skill-based. The study used a pre-test--post-test design and compared the development of English word recognition in the two groups, at the same time controlling for the amount of prior EFL instruction and out-of-school exposure to English. The performance at pre-test was already high, particularly on cognates. Word recognition in the control group did not improve over the course of the 14 weeks. The performance of the intervention group showed significant improvement from pre-test to post-test. After the intervention, they recognized not only more of the words practised in the lessons but also more nontreated cognates, which demonstrates that the intervention participants developed a cognate strategy that allowed them to recognize more English words based on similarity to Dutch. We conclude that explicit cognate instruction implemented in a regular classroom setting facilitates the development of EFL vocabulary in special primary education.