This research investigates the effectiveness of utilizing analytic rubrics in peer-assessment (PA) and self-assessment (SA) methodologies to enhance the proficiency of English as a Foreign Language (EFL) students’ essay writing skills in the Vietnamese context. It further contributes to the existing body of literature regarding formative assessment and its potential to improve student learning outcomes. A total of 44 university students, all English majors, were divided into two distinct groups, each consisting of 22 participants. One group applied analytic rubrics for SA, while the other used the same tool for PA. The writing performance of the two groups was assessed and compared in pre and post-tests. The findings revealed no significant difference between the SA and PA groups in the pre-test. However, in the post-test, the SA group demonstrated significantly superior performance compared to the PA group, with noticeable improvements across all evaluated criteria. Moreover, these results showed that the use of analytic rubrics in SA and PA methods positively impacted the EFL students’ writing skills, particularly in the areas of content and language use. This has practical implications for teachers, curriculum developers, and policymakers in designing and implementing formative assessment strategies for EFL learners. Further research is needed to examine the long-term effects of employing analytic rubrics, and to understand the potential influence of other contextual factors on student learning outcomes.