There is controversy on the conditions under which cooperative learning methods can improve academic achievement. Group-specific motivational aspects might contribute to the effectiveness of cooperative learning among which classroom goal structures were focused on. More specifically, the study aimed at investigating the efficiency of cooperative writing technique through performance versus mastery-oriented classroom goal structures in improving academic writing of Iranian intermediate EFL learners. To this end, 83 intermediate EFL learners took part in this quasi-experimental pretest, post-test study. The participants were required to write a 5-paragraph essay for pretest and post-test. The collected data was analyzed based on an analytic writing rubric (Hedgcock & Leftkowitz, 1992). The results of one-way ANOVA tests indicated that the experimental group which practiced cooperative writing through performance goal orientation outperformed the individual and mastery-oriented classes. It was concluded that performance goal orientation, between-groups competition, and extrinsic motivation, can help EFL teachers in setting a more effective classroom structure for cooperative writing practices to improve the writing proficiency of L2 learners.