The purpose of this study is to clarify the changing process and characteristics of the time frame between the moment of the dualization policy of the teacher evaluation system being emerged as the policy agenda and the moment of it being selected as a policy with a binding force. The policy was analyzed through documentary and interview surveys with Kingdon’s multiple stream model as the basic analytic frame. Research results are as follows. First of all, various problems on the pluralistic teacher evaluation policy, such as inefficiency, low reliability, and teacher workload, were constantly raised. Alternatives were proposed however, it did not lead to policy improvement. Secondly, many stakeholders have put pressure on the government, but the political incident of the 18th presidential election, in particular, has led to the transition of the teacher evaluation dualization policy to the governmental agenda. Lastly, in 2015, a policy window was opened to hold a public hearing for the improvement of the teacher evaluation system. Then, under the leadership of the Korean Ministry of Education, the policy for the dualization of the teacher evaluation system was turned into an official policy of the government. This study shows that the policy changes as a product of uncertainty affected by the flow of politics under contextual conditions. Based on the results of the study, the implications for educational policy makers and researchers were suggested in setting policy agenda and decision making.