A large number of single research studies on the effects of strategy-based instruction (SBI) teaching English as a foreign or second language have been conducted so far. However, the lack of a comprehensive meta-analysis of experimental studies targeting the effectiveness of English language SBI is observed. Therefore, this study aimed to meta-analyze the effects of SBI experimental studies conducted in the field of learning English as a foreign or second language to clarify the aroused controversial issues regarding their overall effectiveness and their related variables. After a comprehensive search to collect the population of experimental SBI of English language studies, effect sizes under random effects model in terms of Hedge’s g were calculated for 26 primary studies, contributing a total of 84 independent effect sizes. The findings indicated that summary effect size of studies with learners at different proficiency levels turned out to be bigger than 0.60. Furthermore, SBI in English as a foreign language context was more effective than the one under English as a second language context. Finally, SBI study samples with treatment time of more than two weeks and English language learners over the age of 14 were more effective than those with less than two week treatment time and learners under the age of 14.

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