Despite the large number of studies on written corrective feedback, there seems to be no consensus among the scholars on the effects of feedback on Foreign Language Learning (FLL) in general and L2 writing in particular. Therefore, there is a need for more well-designed studies to reach a firm conclusion (Ferris, 2004; Guenette, 2007; Sheen, 2007). Using a pretest-posttest design, the present study examined the effects of written corrective feedback in the form of indirect and dynamic feedback, on grammatical accuracy of Iranian EFL learners in academic writing. For this purpose, 56 homogenous EFL learners were selected based on the result of an OPT test, an academic grammar test, and a writing test. They were randomly assigned to two intact experimental groups (n= 20 in each group) and one intact control group (n= 16). The treatments included 10 sessions lasting of writing over 12 weeks. The participants were to write six different paragraphs. The only difference between the experimental groups and the control group had to do with correction; the former received feedback and were required to revise their work based on the provided feedback. The students’ writing and grammar tests were scored by three raters and their writings were coded by two other raters based on Paulus’ (1999) rating scale, academic grammar rubrics and error ratio. The treatment effects were finally evaluated through comparing their scores on the pretest and posttest. The collected data were analyzed and compared using T-test and ANOVA. The findings revealed that the experimental groups outperformed the control group on the delayed posttest. Furthermore, dynamic feedback proved more effective, though not statistically significant, on the immediate posttest while indirect feedback produced better effects, though again not statistically significant, on the delayed posttests. Possible explanations of the results, instructional implications, and applications for the language classroom will be discus
