Enhancing English argumentative writing skills through the Appraisal framework: An empirical study at a Vietnamese university

English argumentative writing remains a significant challenge for many non-English major students in Vietnam, particularly in expressing stance, constructing coherent arguments, and engaging with alternative viewpoints in academic texts. Although the Appraisal framework within Systemic Functional Linguistics has been widely applied in discourse analysis, its pedagogical application in English writing instruction for Vietnamese EFL learners remains underexplored. This study investigated the effectiveness of explicit instruction in the Appraisal framework, particularly the Engagement system, in improving students’ argumentative writing. A quasi-experimental design was employed with 60 Vietnamese university students. The experimental group ( n = 30) participated in a 12-week writing course incorporating explicit instruction in Appraisal resources, while the control group ( n = 30) received conventional writing instruction. Data were collected through pre- and post-test argumentative essays. In addition, students in the experimental group completed a questionnaire to evaluate their learning experiences with the Appraisal-based instruction. The findings revealed that the experimental group achieved substantially greater gains in the use of Engagement resources than the control group, with overall Engagement frequency increasing from 2.02 to 6.99 compared with 2.13 to 4.26 in the control group. Questionnaire responses further indicated positive perceptions of the Appraisal-based instruction. The study provides empirical evidence for the effectiveness of the Appraisal framework as a pedagogical tool for developing argumentative writing competence and supports its integration into EFL writing instruction for non-English major students in Vietnam.