Teachers in Korea commonly integrate academic subject content and language teaching, an approach whose efficacy has not yet been firmly established. This presentation will explain a research project on perceived efficacy of different academic subjects used in content and language integrated learning (CLIL). The project targeted both current and former students of a public Korean high school CLIL program and examined their perceptions of CLIL efficacy across six subject categories. A quantitative survey approach was employed to collect data from a large number of students (N = 123). The collected ordinal data was analyzed using non-parametric statistics, revealing multiple significant differences with large effect sizes (r equivalent > .9) in perceived efficacy among pairwise comparisons of the academic subjects. The presentation will also outline how these initial findings will be valuable to teachers and program designers and present paths for additional research necessary to establish CLIL efficacy for the Korean context.