"Sansu" and "Sugaku"

This week, many elementary schools in Japan held graduation ceremonies.

In Japan, new grade starts from April, and 12 year-old students start junior high school.
By the way, Japanese have different names for "mathematics" in elementary school and in junior high school and above. In elementary school it is "Sansu," and in junior high school and above it is called "Sugaku."
We assume that the different names show that a special meaning is given to students' firm understanding of the basis of arithmetic, figures and measurement in elementary school. "Sansu" serves as essential tools for daily life, not just as a foundation for algebra and geometry to be learned at junior high school and above. Some say that "Sansu" is to understand and practice one plus one is two, and "Sugaku" is to contemplate and explain why one and one is two. This view may be quite true.