As writing skill is considered important in globalised societies nowadays, the skill is taught and assessed in English classrooms in Korea. As for assessment, however, there are no authoritative rating schemes suggested for classroom testing contexts. Given this lack, this study investigates the applicability of one of the existing scales, the FCE rating scale for writing assessment, to Korean high school contexts through both theoretical considerations and an empirical study. From both the theoretical perspectives and the empirical study, in which three English teachers at Korean high schools were asked to assess 6 writing samples using the FCE scale and to do think-aloud during the assessment, it was found that the FCE scale in this context tends to cause problems for the validity of the assessment. It was, therefore, concluded that, for the sake of validity, this kind of scale cannot be applied to the context for which it was not developed, and that there is a need to develop a rating scale, taking into account the characteristics of test-takers, raters and assessment context in question.