This study aimed at comparing the impact of teacher-selected vs. student-selected discussion groups on speaking fluency of extrovert vs. introvert Iranian EFL learners. In order to do the study, 80 homogenous students were selected from among 140 intermediate female English language learners through the Oxford Placement Test. Then they were divided into introvert and extrovert learners based on the results of the extrovert and introvert questionnaire, and they were totally divided into four groups, namely extrovert student-selected, introvert student-selected, extrovert teacher-selected, and introvert teacher-selected. The participants in all groups took part in the speaking pretest. To do the discussion activities during the treatment process, the participants in the student-selected groups choose their groupmates themselves, while in the teacher-selected groups, the group members were chosen by the teacher. Finally, the participants took part in the posttest of speaking, and the obtained data were analyzed. The results of the analyses showed that selecting discussion groups by both students and teacher affected speaking fluency of extrovert and introvert learners. The results also confirmed that extrovert learners, in both student-selected groups and teacher-selected groups, outweighed the introvert learners regarding their speaking fluency. Teachers are, therefore, recommended to use both teacher-selected and student-selected discussion groups in their classes. They are also recommended to encourage introvert students to take part more actively in class discussions to obtain better results in improving their speaking.
