Despite considerable evidence that supports the use of grading rubrics (GRs) as tools for written corrective feedback, there is a paucity of research that investigates which of the different types of GRs best develops learners' International English Language Testing System (IELTS) writing scores in English as a medium of instruction (EMI)-contested settings. This study attempted to explore which rubric types (i.e., holistic, ESL composition profile, correction code, and IELTS) best assist English as a Foreign Language (EFL) learners in writing proficiency and which type leads to improving IELTS scores when such practice is embedded in EMI-disputed settings. Therefore, 351 male and female Saudi EFL learners were recruited to participate voluntarily. These participants were distributed equally among four groups corresponding to rubric type. For almost four months, the participants were exposed to a process-genre approach in which they were required to draft topics based on the comments received from their peer colleagues and teacher. The comments provided depended on the rubrics specified for their group type. The participants' pretest, midterm, and posttest scores were analyzed using one-way analysis of variance, t-tests, and paired samples t-tests. The results revealed that the ESL composition profile developed gradually, followed by the correction code group. However, the holistic groups did not improve. The tests were also assessed by specialists using the IELTS rubric. The findings revealed that the IELTS groups outperformed the other groups in all tests, followed by the female group in the ESL composition profile in the posttest. Meanwhile, other groups failed to improve. We discussed the results, considering the importance of GRs for improving EFL learners’ scores. Finally, we outlined the pedagogical implications for writing teachers in EMI settings. This study aimed to contribute to the growing research on EMI in relation to GRs, especially in the context of tertiary education in Saudi Arabia.