Abstract Writing is a basic communication skill and a unique asset in the process of learning a second language.” (Chastain 1988: 244). This study considers the effect of grammatical error correction on the development of English writing among Persian learners of English as a foreign language. The participants of the study are forty students at the age of 17 – 22 fourteen male and twenty six female. The subjects were divided into control and experimental groups. A pretest was carried out to have homogenous groups. After the pretest the subjects were asked to write samples about given topics. Each student wrote ten samples. The period of instruction lasted for twelve weeks. Both groups received grammatical error correction, and the errors were identified with red pen for both groups. However, the experimental group received a detailed list with clarification and the possible accurate answer. Moreover, an oral explanation was given to them at the time of delivery of the samples. They were also asked to pay attention to the comments. Concerning the control group, after viewing their grammatical error their papers were collected and kept by the instructors, whereas the experimental group kept their papers. Finally a post test was carried out to assess the results. The post test includes two writings about the topics suggested by the instructors. They have to write one at home and one in the class within twenty five mints. Two raters were used to correct the final tests. The results of the post tests show that there is difference from number of the errors for the sample written at home, but the difference is not significant with the samples written in the class under time pressure.

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