Research on pre-task planning has revealed that planned conditions have produced more fluent and complex language than unplanned conditions. To date, most of these studies have investigated the effects of individual planning on language production while collaborative planning has received scant attention. To determine the effects of pre-task planning on second language written production, the present study examined Iranian EFL learners’ argumentative writings under the conditions of individual and collaborative pre-task planning. The participants’ written productions were analyzed using three measures of fluency, complexity, and accuracy. The performance of individual planners and collaborative planners were compared using a series of one-way ANOVAs. Results indicated that collaborative planning promoted more accurate textual output while individual planning resulted in greater fluency. The results obtained from one-way ANOVAs also revealed that neither type of planned conditions benefited complexity. Possible explanations are provided and the implications of the findings for the applicability of collaborative planning are discussed.