In this paper I analyze and evaluate the changes which have occurred in the curriculum policies and lesson studies of twentieth century Japan. Formulated and implemented in the late nineteenth century as part of the social reforms of the Meiji era, lesson study was much influenced by the Western pedagogy of the time, and was intended to increase bureaucratic control and promote research among teachers. Under the influence of Pestalozzian developmentalism and Herbartianism, Japanese education became more progressive during the Taisho era (1912-1926). Progressive education and its lesson study practices have developed into a grass-roots movement in Japan. Despite of its popularity, progressive education has been criticized for lacking empirical evidence, and though it is not an American-style quality circle, some try to explain it in those terms. For instance, progressive education has been labeled as a cause of the ”mediocrity” of Japanese students. Another cause for concern in contemporary Japan is widening inequality, and many scholars of educational sociology see a link between social class differences and the practices of progressive education. Nonetheless, even though lesson study has mainly been developed by progressive educators in Japan, it has not been targeted by these politically motivated attacks. In the final part of this paper I delineate the contemporary forms of lesson study in terms of newly elaborated concepts such as the behavioral objectives approach and the learning community.