Who should disseminate new curriculum and textbooks from the central government to classroom in developing countries? And, how is it possible? Curriculum and textbook developers often faces the necessity of and the challenges in spreading the essentials and intention of new curriculum and textbooks and the expected educational practices to classroom. In order to design and implement consistent educational reform through three layers of the curriculum (the intended, the implemented and the attained level), it is required for them to be committed in not only the development stage with a clear picture of quality teaching and learning, but also the dissemination stage through in-service teacher training such as lesson study. This study aims at clarifying potential measures to develop the expertise for curriculum and textbook developers as a communicator of educational reform in developing countries. In the process of our project on the curriculum and textbook development of social studies education in Cambodia, we assume “the expertise of consulting lesson study” and examine it both from theory and practical cases of (i) lesson-demonstrating approach and (ii) lesson-advising approach. As a consequence, it is found that their ability for consulting lesson study could be enhanced by regarding senior (Japanese) experts as a role model. And also, the result implies that, for their continuous professional development, it is necessary for them to purposefully take part in lesson study consulting, and shift the approach from “modeling” to “coaching” by steps.