||Kim, Hye Jeong. (2019). Customized mobile application based on learners’ different levels in the EFL classroom: Efficiency and value of apps. The Linguistic Association of Korea Journal, 27(1), 42-62. The aim of this study is to explore the influence of a customized mobile application developed for a certain liberal arts class and to consider learners’ attitudes and perceptions about using customized mobile apps in the classroom. An experimental group and a control group were classified into an upper and lower group, respectively. I and II tests were conducted to determine the impact of the use of classroom-specific mobile apps. Individual interviews and an open questionnaire were carried out to identify learners’ attitudes and perceptions. The results of the study indicate that more adept learners were not significantly affected by the learning method (i.e., the mobile app or the handout), whereas less adept learners were more likely to benefit from learning through the mobile app than through the general handout form. The results from the interviews and open surveys suggest that mobile apps can: (1) create interest and motivation for learning; (2) be conveniently used beyond time and space constraints; (3) are great learning tools; and (4) ease the burden of studying. In order to support mobile usage in the classroom, more experimental research regarding the efficiency and learning effects of mobile apps should be carried out in the future.