One consequence of test use in the English-language teaching community is the negative washback of tests on teaching and learning. Test preparation courses are often seen as part of the more general issue of washback. IELTS and TOEFL iBT tests, focusing on communicative competence, are anticipated to have positive washback effect on how English is taught and learned. This study was a triangulation research to compare the washback of IELTS and TOEFL iBT on teaching and learning activities in test preparation courses. To this end, questionnaires survey with 40 IELTS and iBT teachers, 220 IELTS and TOEFL iBT students, and also ten class observations and ten teachers' interviews were called upon and the related data were analyzed quantitatively and qualitatively. The results showed evidence of both negative and positive washback in the relevant courses. Generally, in both courses the class time was more characterized by the negative influence of the test although IELTS classes seemed to promote more positive washback than TOEFL iBT did on class activities. While the TOEFL iBT preparation courses appeared to address a wider range of activities for academic study, IELTS preparation courses provided more opportunities for learners' interactions and communications in line with the test activities.