This study aimed to investigate the impact of task sequencing, along +/- reasoning demands dimension, on writing task performance in terms of accuracy. The study was motivated by Robinson’s Cognition Hypothesis (CH) as well as previous studies investigating the relationships between task complexity and second language production. The participants of the study were 90 intermediate students at the Islamic Azad University, Shahr-e-Qods Branch, chosen from three classes based on their performance on the Preliminary English Test (PET). The participants in the three classes were assigned to three groups: Experimental 1, Experimental 2, and a Control group. At first, the students in all groups took part in the writing pre-test. Next, the treatment sessions including 8 sessions of picture description task performance began, during which the first experimental group received a series of picture description tasks based on a randomized order of cognitive complexity. The second experimental group received the same tasks, but ordered from simple to complex, based on their required reasoning demands. The control group, however, received some writing activities from the course book. Finally, during the last session, the post- test was administered to all participants. The results of the data analysis showed a significant positive impact for sequencing tasks from simple to complex on accuracy in writing task performance.
