The purpose of this study is to describe the 26-year(1924-1950) process of the Jena- plan by focusing on the character of the Jena University School as an experimental school, and to clarify a new image of the Jena-plan in response to the discourse that it was stagnation after the 1930. Petersen’s attempt at the school reform, which began in 1924 and ended in 1950, experienced three different political regimes: the Weimar period(1924-1933), the Nazi period(1933-1945), and the Soviet occupation /German Democratic Republic period(1945-1950). Therefore, the Jena-plan has been understood by each time periods by the political system of the time. After 1930, the Jena-plan played an important role as an experimental school, both outside the Jena University School in its expansion to various schools, and inside the Jena University School in its pedagogical factual research(pädagogische Tatsachenforschung). Furthermore, it became clear that the faculty organization of the Jena University School did not continue to be transformed, but that attempts to reform the school based on pedagogical factual research continued.