The Linguistic Association of Korea Journal, 26(1), 23-55. Although formative feedback has been shown to be beneficial in L1 writing classes, the benefits of formative feedback for critical writing in EFL context have not been widely explored. The aim of this study is to determine which factors are more effective in improving EFL students’ critical writing. The study was conducted in an intensive English reading and writing program with 134 university students divided into two intermediate and two beginner level classes. The researcher provided formative feedback over the course of the semester. Analysis of the critical writing achievement test measured from writing collected at the beginning and end of the course revealed that the experimental group (EG), which received formative feedback focused on their critical writing, made more meaningful gains on the writing achievement test than the control group (CG), which had only corrective feedback during class. Results also demonstrated that students at the beginner level in the EG improved more than those at the intermediate levels on the writing achievement test. In addition, learners at the beginner level in the EG made gains in both micro and macro aspects of critical writing, while those at the intermediate level improved only macro aspects of their critical writing. Both the intermediate and beginner groups made similar gains in criticality.