The use of task-based collaborative output activities in enhancing EFL students’ writing proficiency has been underrated in the Iranian context. To foster students’ writing ability, the present study, employing a mixed-methods design, aimed to evaluate the effect of innovative tools, dictogloss and debating, on the writing development of English-major university students in terms of complexity, accuracy, and fluency (CAF). The study involved two experimental extracurricular classes and consisted of 11 sessions during the regular academic term. Having analyzed the writing tasks produced by the students’ performance on pre-test and post-test, the researcher found that the students of both groups significantly enhanced their writing performance, representing an increase in a number of indices of CAF measures following the intervention. More specifically, the results of a paired-samples t-test confirmed that the students in the dictogloss group showed significant improvement in six indices of CAF measure, and the students in the debate group displayed significant improvement in seven indices of CAF measures. Moreover, the results of ANCOVA confirmed that the debate group improved more than the dictogloss group in terms of CAF measures. The results of the interviews with the students regarding the role of task-based collaborative output activities in their written performance yielded several commonalities, which were coded into 11 codes for dictogloss and 16 codes for debating, taking inter-coder reliability and agreement into account. In the end, the study offers some practical implications for L2 learners and teachers.
