the effectiveness of strategy-based instruction in teaching english as a second or foreign language: a meta-analysis of experimental studies

a large number of single research studies on the effects of strategy-based instruction (sbi) in teaching english as a foreign or second language has been conducted so far. however, the lack of a comprehensive meta-analysis targeting the effectiveness of english language sbi is observed. moreover, the findings of experimental studies regarding the context of the english language, proficiency level of the english language learners, the treatment time, the strategy types used in each study, age of english language learners, and outcome measures of each study have not been meta-analyzed so far. 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 the related variables mentioned above. to do so, a comprehensive search was conducted to collect the population of experimental sbi studies. effect sizes under both fixed effect and random effects models in terms of hedges g were calculated for 26 primary studies, contributing a total of 84 unique samples. the findings indicate that the overall summary effect size of study samples under both models was larger than 0.718. in addition, the summary effect of studies with different outcome measures was greater than 0.424. besides, the summary effect size of studies with learners at different proficiency levels turned out to be bigger than 0.689, with the learners at the advanced level having the largest summary effects under both models. furthermore, the comparison of the sbi study samples under english as a foreign language context and english as a second language context showed that sbi under english as a foreign language context was more effective than the one under english as a second language context. also, sbi study samples with treatment time of more than two weeks were more effective than those with less than two week treatment time. moreover, study samples with different strategy types for sbi ranged from 0.46 to 1.46. finally, study samples with english language learners over the age of 14 had larger summary effects than those with learners under the age of 14.