This paper demonstrates that genre-based pedagogy can contribute to the improvement of students' English skill especially argumentative writing skills which are needed in assessment practices of English test proficiency such as IELTS. To reach the goal of the study, a qualitative research design was used. Specifically, a qualitative case study was employed since, in this study, the writer presented detailed linguistic analyses of student's writings. The data was a collections of students' writings in various stages, which were then analyzed using the framework 3x3 matrix developed by Humprey and her colleagues (Humprey, Martin, Dreyfus, & Mahboob, 2010) within Systemic Functional Theory (hereafter SFL). The findings showed that the students' argumentative writing skills improved; the students could write argumentative texts with clear schematic (level of genre) and use linguistic resources well (level of discourse) after teaching program.