The purpose of this study is to provide raw data for performance assessment policy. For this purpose, we adapted two methods. One is content analysis about performance assessment policy, the other is in-depth interview and participatory observation about teacher's practical knowledge in relation to execution of performance assessment. The results of this study are summarized as follows. In relation to performance assessment policy, there are practical irrelevance, logical irrelevance in content that prescribed paper assessment based on taxonomy, problem relation with criteria of performance assessment. Regarding to the relationship between the performance assessment policy and teachers' knowledge on the performance assessment practice, teachers seemed to have the difficulties in dealing with situations with complicated practical problems. It has made these teachers focus more on practical problems rather than the purpose of performance assessment. It has resulted from the existing conditions in their schools, compulsory nature of performance assessment, and the rule requiring unreasonable objectivity. Then, the performance assessment policy would not be accompanied with teachers' voluntary participation and result in superficial, restricted, short-term practice. This study suggests that internal validity needs to be fulfilled in establishing the performance assessment policy. Secondly, practicality must take precedence in the performance assessment policy. Finally, institutional support must be achieved to improve teachers' professionalism and autonomy.