fa The Impact of Interactive Output Tasks on Developing Vocabulary Knowledge of Iranian EFL Learners پژوهشي Research <div style="text-align: justify;">This study investigated the role of interactive output tasks in developing EFL learners&rsquo; vocabulary knowledge. The participants were 103 elementary female Iranian EFL learners who were randomly divided into three groups: input-only, input-output-no-interaction, and input-output-interaction. After all participants took a placement test and a vocabulary pretest, the input-only group was exposed to input tasks, while the other two groups received both input and output tasks with or without interaction. Then, all the participants took a vocabulary posttest. The results of ANOVA and Kruskal-Wallis tests showed that the participants in both the input-output-no-interaction group and the input-output-interaction group outperformed the ones in the input-only group in the vocabulary posttest (in both the overall vocabulary test and in the productive vocabulary section). Moreover, the results of the <em>t</em>-test and the Mann-Whitney test revealed that the participants in the interaction and no-interaction groups performed similarly on both the overall vocabulary posttest and the productive vocabulary section. The findings of this study support the idea that output is a facilitative factor for the acquisition of L2 vocabulary and, specifically, productive vocabulary development. The results also suggest that both interactive and non-interactive output-plus-input tasks can lead to higher achievement in vocabulary knowledge compared to the input-only condition lacking output tasks.</div> Vocabulary , Output , Interaction , Productive vocabulary , Input , EFL learners , Vocabulary , Output , Interaction , Productive vocabulary , Input , EFL learners 93 113 http://ijal.khu.ac.ir/browse.php?a_code=A-10-3-59&slc_lang=fa&sid=1 Zahra Mahmoudabadi 1003194753284600901 1003194753284600901 Yes Payame Noor University, Tehran Hassan Soleimani 1003194753284600902 1003194753284600902 No Payame Noor University, Tehran