Researchers have extensively studied factors that impact the development of fluency in L2 oral production while there is scant evidence regarding task variation-related effects. Therefore, this study sought to investigate the effects of task variation involving group dialogue, dialogue unscrambling, and dialogue completion on Iranian EFL learners’ oral speech fluency. To this end, 80 EFL learners were assigned to three experimental groups (EXG1, EXG2, and EXG3) and one control group shown as CONG. The EXG1 was treated by three tasks, i. e., dialogue completion, dialogue unscrambling, and group dialogue, the EXG2 through two tasks involving dialogue completion and dialogue unscrambling, the EXG3 by dialogue unscrambling task, and the CONG was instructed by teacher conventional method. The groups were pretested and posttested through the speaking section of Preliminary English Test (PET). The participants’ interview transcriptions were then coded for scoring and statistical analysis of fluency to show the effects of treatment for each group. The four groups received their required instructions for ten sessions. The findings revealed that task variation made significant differences in the learners’ oral fluency achievement. The analyses made through running ANOVA and Post Hoc yielded to the conclusion that EXG1, instructed through a combination of the three tasks, outperformed the other groups regarding fluency achievement. The findings of this study have pedagogical implications for teachers, EFL learners, and syllabus designers.
