Aristotle’s concept of “ethos” is commonly known as “credibility” in the modern persuasion theory. In Speech and Composition, one of the general elective subjects in the modern contemporary Korean Language Education Curriculum, deals with achievement standard related to “credibility”. The purpose of this study is to investigate how Korean language teachers evaluate on the ‘Peer assessment cases of high school students considering credibility’ and how they do achievement standard in the Korean Language Education Curriculum relating to credibility. This paper also proposes several solutions to issues of credibility in Korean Language Education. The main sources of data for this study include the results of oral speech evaluations and surveys by Korean language teachers. In order for the teachers to understand the context of this study sufficiently, a copy of the corresponding talk and the peer assessment result sheet were provided by e-mail or in hard copy; teachers were then asked to complete the evaluation and participate in the survey “Peer assessment cases considering credibility”. By analyzing the responses of 23 Korean language teachers, this study explores issues relating to credibility in education.