Stimulated by the discussions of the Third International Mathematics and Science Study (TIMSS) and the TIMSS Video Study of mathematics classrooms in Germany, Japan and the US this paper shows that we cannot limit observation to mathematics lessons in Japanese public schools when we want togain insights intothe achievement of Japanese students. Homework, voluntary studies at home, and private supplementary lessons are more important in Japan than in Germany or in the US. Japanese students not only invest much more time in mathematics but they are also intensively supported and guided professionally. Moreover, the aims and methods of the teaching and learning processes organized privately complement the mathematics curriculum in the public schools. Findings of empirical investigations give evidence that parents and supplementary schools contribute substantially to the learning success of Japanese students.