The current study investigated the effect of collaborative prewriting activities on learners’ identity construction and L2 writing development. To this end, 43 sophomore upper-intermediate university students majoring in Teaching English as a Foreign Language at an Iranian university who had enrolled in a course called Advanced Writing were randomly divided into two experimental groups (groups A and B) and one control group (group C). While the students in group A were involved in group activities, the students in group B were engaged in pair activities. The students in control group (group C) worked individually. As a pre-test, a pen-and-paper writing task was given to all the students at the beginning of the semester. During the semester, all the participants were exposed to the same materials and were taught by the same teacher for one semester. The only difference was the type of activities in which the participants were engaged. At the end of one semester, a pen-and-paper writing task was given to all the three groups. The findings of the post-test revealed that all the students could significantly improve their writing skills. Nevertheless, the students in group B significantly outperformed their counterparts. Most importantly, the results of identity analysis showed that the students in group A used authorial plural pronouns along with adjectives more frequently.  The findings of this study confirmed two issues: first, the significant efficacy of prewriting activities were confirmed at the end of the semester. Second, each type of prewriting activity could affect the learners’ identity construction.