Whilst diary study is used for pedagogical purposes, course evaluation and basic research on language learners, this study aims to explore the possibility of using it to investigate how teachers perceive and use rating schemes. Three English teachers who worked at various high schools in Korea rated 224 scripts written by 112 Korean high school students for this study. The teachers assessed the scripts twice, first according to their subjective holistic scoring and then using the FCE scale for writing assessment, and they kept diaries on their rating process for each assessment. The analysis of their diaries shows the teachers' rating patterns and tendencies, problems with the rating schemes and their understanding of the rating schemes. It can be concluded from these findings that diaries can be employed with regard to assessment, that is to reveal raters' perception of rating schemes, to investigate the validity of the assessment and to identify the aid and guidance that they might need for assessment. (Contains 3 footnotes.)