This study aims to analyse factors which accelerate or decelerate sexual activities among teenagers of highschool age in Japan and discuss what is important in planning sexuality education in schools. Since the 1990s,sexual behaviours among youth have changed considerably in Japan.First, an overview of the previous and current situation of school-based sexuality education in Japan isprovided. We discuss how Japan has been reluctant to promote sexuality education and has not taken accountof perspectives in gender, sexual health, and rights.Second, the nationwide data gathered in Japan every six years from 1993 to 2011 by multivariate statisticaltechniques is analysed. The results show that the home environment, sexual images, and gender norms havean impact on sexual behaviours. The gendered division of labor is a norm that has a greater effect on recentteenagers' rate of having sexual intercourse than it did on those from the previous decade. The norm that menshould take the initiatives in intimate relationships has a strong impact on girls.Thus, we conclude that it is essential to approach comprehensive sexuality education from a genderperspective by involving family, community, experts, and practitioners in conducting peer-group sessions.