Argument maps as schematic representations of arguments and their logical and evidential relationships are effective diagrams for instruction in education as well as in L2 development. However, their use for teaching L2 writing in EFL contexts has not been adequately studied. Therefore, this study investigated the effect of argument mapping instruction on Iranian EFL learners’ writing achievement and writing components, including grammar, coherence, cohesion, and task accomplishment in expository and descriptive essays. The participants were 60 intermediate EFL learners at Fadak language institute in Tehran. The selected participants were randomly divided into two groups: an experimental and a control group, each including 30 participants. Materials, coursebooks, and the teacher were the same for the study groups. However, the participants in the experimental group received specific instruction about the use of argument maps before and during their writing. After 10 sessions of treatment, the learners in the two groups were asked to write a descriptive and an expository paragraph. The paragraphs were rated by two raters and the final score was the average of the scores given by the two raters. The results of the data analysis revealed that argument mapping strategies had significant improvement impact on expository and descriptive writing tasks and could improve participants’ writing in terms of grammar, coherence, cohesion, and task achievement. However, argument mapping was not beneficial in improving the vocabulary of study participants’ writing. Findings of the study suggest that EFL language instructors and learners can use argument maps for teaching descriptive and expository writing.
