This study aimed to investigate the impact of teaching developmental grammatical errors on translator trainees’ L2 paragraph writing ability. After the administration of Oxford Placement Test (OPT), 40 out of 100 undergraduate translator trainees were selected from the Islamic Azad University of Tonekabon branch. Further, the participants were divided into an experimental and a control groups. A pre-test of paragraph writing ability was administered to both groups and the participants were asked to write a paragraph about the selected topic. Then, the experimental group received 5 sessions of treatments on teaching developmental grammatical errors extracted from their previous writing performance while the control group received a placebo. After five sessions of the treatments, the post-test of paragraph writing ability was administered in which the participants in both groups were asked to write a paragraph about a selected topic. Three raters corrected the paragraphs. The scores were analyzed using the SPSS software by applying Independent sample t-test and Pearson correlation. The findings indicated that subjects in the experimental group showed significant improvement in their writing performance.
