Studies have shown that language tests can and often do have powerful influences on teaching, learning, and the creation and dissemination of educational materials, such as textbooks, in addition to the formation and implementation of language education policies (Au, 2007; Alderson & Wall, 1993; Bailey, 1996, 1999; Cheng, 2008). While the literature provides evidence for this influence, collectively described as ‘impact’, or more specifically, ‘washback’, the form and intensity in which it occurs differ greatly across contexts, due to the dynamic and complex nature of washback phenomena. This case study investigated the washback effects of an English language speaking test, the GMATE (General Multimedia Assisted Test of English), used as an exit examination in a large university in Seoul, South Korea. Developed from the Washback Hypotheses (Alderson & Wall, 1993, p.120-121), there were two main research questions answered through this study: 1) What are the perceived washback effects of the GMATE on teachers’ teaching? 2) What are the perceived washback effects of the GMATE on students’ studying? To answer these and related sub-questions, a mixed-methods approach was taken, including questionnaires, interviews, and classroom observations. This provided a clear picture of what was occurring in this particular context, while offering a voice to the 459 students and 17 teachers who participated in the study. The findings of this study showed that the GMATE indeed had washback effects on the teachers and student participants, and that these effects varied depending on students’ proficiency level, year in school, and term of study. Furthermore, these results supported the notion that washback is highly contextual (Cheng et al., 2014; Cheng, Sun, & Ma, 2015; Cheng, Watanabe, & Curtis, 2004), as this thesis highlighted the importance of bearing in mind sociocultural factors that may contribute to washback effects in this and other unique research contexts.