Ability grouping--defined as a practice that places students into classrooms or small groups based on an initial assessment of their readiness or ability--has received considerable attention in educational research for years in many countries (Ireson & Hallam, 1999, 2001; Slavin, 1987). In Korea, ability grouping has been implemented in elementary, middle, and high school settings for certain subjects such as English. The purpose of the current study was to determine how the ability grouping policy has been implemented in Korean middle school English classes and to examine the perceptions of teachers (n = 55) and students (n = 754) regarding this policy. The results showed that schools implemented the policy in a variety of ways (e.g. different number of grouping levels). Teachers and students indicated their concerns regarding students' emotional problems and showed mixed attitudes towards ability grouping. They also argued that schools need large support to maximize the putative effectiveness of ability grouping in different areas such as curriculum design, materials development, and teacher training. The findings are discussed in terms of pedagogical recommendations for increasing the effectiveness of ability grouping in English classes and other options for future research to investigate this and relevant educational language policies. (Contains 1 figure and 4 tables.)