This study investigated how group formation method, namely student-selected vs. teacher-assigned, influences group dynamics as well as group outcome. In line with its experimental comparison group design, two intact classes of junior English Literature students (N=32) participated in this study over one academic semester. Community model was employed to teach creative writing to both classes, but, while in one class students (N=16) were required to self-select their working partners, in the other they were assigned into groups by the teacher, based on their learning styles (N=16). The quantitative and qualitative data, obtained through students' initial writing drafts, revised texts and an end of the course written report, underwent One way Analysis Of Variance (ANOVA) and content analysis. The findings indicated that although teacher- assigned groups had no definite advantage over those of student-selected in terms of group dynamics, they noticeably outperformed student-selected groups in terms of outcome. In particular, teacher-assigned groups were more task oriented and thus more successful at accomplishing group task -here revision. The results suggest that group formation method is a contributing factor to the success of group work.