The purpose of this paper is to examine the process of reduction in class size and then to analyze the effect of the reduction in Japanese primary and junior high schools from 1959 to 1999. The findings are as follows:

1. Class size reduction has been affected by the total number of pupils and students: the reduction was dramatical when the total number decreased; where as the reduction declined when the total number increased.

2. Class size reduced dramatically during 1960s and modestly during 1980s and 1990s.

3. "The Improvement Plan on Teaching Staff Deployment" policy has played a significant role in improving the educational conditions in schools.