This study explored the washback of TOEFL iBT on Korean teachers and students in commercial language institutes in Korea. Firstly, it observed the participants ' perceptions and attitudes towards TOEFL iBT and secondly, their teaching and learning practices in test-preparation classrooms. 194 adult students participated in the survey, six of whom were interviewed. Seven teachers participated in the research: four in classroom observations and questionnaires and six in interviews. Qualitative data were analyzed with Saldana's (2009) coding methods using NVivo 9 and quantitative data were analyzed using SPSS 19. The findings show that the participants had positive attitudes towards note-taking, the exclusion of the Structure section, the usefulness of the Speaking and Writing sections, and the validity of TOEFL iBT. However, some participants were negative about the addition of accents in the Listening section, the testing methods, and the Speaking and Writing sections. Their learning and teaching methods were various depending on the individuals. However, the general learning methods were highly focused on improving test scores and the Speaking and Writing classes were the same as typical test-preparation classes. Thus, some positive washback on teaching and learning were found. However, the participants' approaches towards the Speaking and Writing sections were limited to mastering test-taking strategies. It is proposed that this study will be useful for test-developers, such as those in the ETS (Educational Testing Services) and the KICE (Korean Institute for Curriculum Evaluation) in terms of designing English proficiency tests. In addition, the findings indicate the importance of teacher training for teachers conducting test-preparation classes.