Among the latest efficient approaches in language teaching, Task-based Language Teaching has turned up to be the main approach in a way that it is currently recognized as the leading teaching approach in language instruction (Ji & Pham, 2017). Using the proper tasks based on the proficiency level of the learners can facilitate the process of language learning. The present study aimed at investigating the effect of open and closed tasks on improving Iranian EFL learners’ oral performance at intermediate and advanced levels. This study is a quasi-experimental research with pretest and posttest design. The participants of the study included 55 female EFL learners at Jahadeh Daneshgahi language institute in Tabriz city, who were selected through cluster random sampling method. The data were collected through 10 open tasks and 10 closed tasks along with an oral pretest and an oral posttest checklist that examined grammar, pronunciation, vocabulary, breakdown-response, interaction, and speech flow of learners’ oral performance. The tasks were selected from the Four Corner series (Richards & Bohlke, 2012). The data were analyzed by a two-way MANCOVA test and ANCOVA. The obtained results indicated that open and closed tasks can improve EFL learners’ oral performance and there is no significant difference between open and closed tasks in developing learners’ oral performance in both levels. Besides, at the advanced level, the amount of oral performance development is greater than the intermediate level. The outcomes of this study can be useful for EFL teachers and learners regarding using the optimal kind of tasks in improving oral performance.
