This study aims to investigate an overall effect of cooperative learning (CL) on L2 learning by providing reliable common effect sizes. The study also examines moderating variables (grade levels, types of CL and instruction time) on language learning ability. For this purpose, a meta-analysis with the software CMA ver.3.3.070 was used. A total 53 primary studies were selected and 163 samples based on means were analyzed to compute the effect sizes. The major findings are as follows: 1) CL is effective to enhance the English ability of Korean L2 learners. The overall effect size is .544 indicating moderate effect size. More specifically the effect sizes of listening (ES=.658) and speaking (ES=.749) are relatively higher than those of writing (ES=.373) and reading (ES=.431). The effect size of attitude (ES=.904) is the highest and that of interest (ES=.624) and motivation (ES=.589) follows in order. 2) There is moderating effect between the types of CL. However, no moderating effect is shown between school levels and instructional time. The effect size of STL(Student Team Learning) and CP(Cooperative Project) is relatively higher than that of STL-CP.
