The present study investigated the impact of language learning strategy instruction on the enhancement of less successful Iranian English as a Foreign Language (EFL) learners’ L2 achievement. To this end, 40 less successful EFL students took part in the study, 20 of whom were trained based on CALLA (Cognitive Academic Language Learning Approach) and the rest formed the control group. A complete TOEFL PBT test was administered to the 40 participants of the study to homogenize them in terms of language proficiency.The results of two independent samples t-tests and two separate paired samples t-tests indicated that explicit strategy instruction had a significant positive impact on L2 achievement of less successful Iranian EFL learners as the participants in the experimental group significantly outperformed their counterparts in the control group. The results of the current study might contribute to the educational policymakers, materials writers, syllabus designers, curriculum developers, and foreign language teachers to incorporate learning strategies in their policies, curricula, syllabi, materials, and instructional tasks if they intend to boost EFL learners’ L2 achievement
