Indubitably, the efficacy of metalinguistic awareness in improving EFL learners’ grammatical knowledge and writing quality has long been an area of great interest in applied linguistics Brown (2001). Accordingly, the main objective of the present study was to investigate the impact of planned and unplanned focus on form instruction on students’ ability to learn grammar and use it appropriately in their writing. For this purpose three intact classes registering for the Grammar and Writing course in university of Isfahan ,Iran were chosen for teaching the target structure (i.e., transitional devices) through different methods of focusing on form instructions. The selected samples comprised 30 in each group, male and female sophomore students with the age range of 19 to 24, studying English translation at university of Isfahan. The samples received instruction through planned focus on form instruction (PFFI), unplanned focus on form instruction (UFFI) and zero focus on form instruction (ZFFI) respectively. The results of the post-test on paragraph writing and on the subsequent delayed post-test revealed that the participants in the planned group notably out performed those in the unplanned and zero focus on form groups in handling transitional markers in the writing of paragraphs.