The current study aimed at investigating the effects of three types of prewriting planning conditions, namely teacher-monitored collaborative planning (TMCP), student-led collaborative planning (SLCP), and individual planning (IP) on EFL learners' computer-mediated L2 written production and learning transfer from a pedagogic task to a new task of similar complexity. To this end, 76 EFL learners were randomly assigned into one of the three groups: TMCP group, SLCP group, and IP group. Two complex letter writing tasks were used in this study to collect the required data: complex task 1 (CT 1) and complex task 2 (CT 2). To perform CT 1, at first, the participants in TMCP and SLCP groups were required to have prewriting collaborative planning via Telegram instant messaging, while the participants in IP group were required to do the prewriting planning individually. To examine learning transfer, one week after they performed CT 1, the participants in the three groups were asked to perform CT 2 for which there was no planning time. The results revealed that (1) the three types of prewriting planning conditions used in the present study promoted different dimensions of the participants' computer-mediated L2 writing, (2) the participants in different groups differently transferred their linguistic abilities to the new task, and (3) factors such as teachers' monitoring and directing students' performance seemed to channel the participants' attention toward specific dimensions of L2 production and hence influenced the quality of their L2 writing and learning transfer. Implications are discussed, and avenues for future research are outlined.