teach all subjects. At my school, all teachers are supposed to show their classes at least once a year and I opened an arithmetic class with teachers of the same grade. The content was trapezoid and its formula.
Area of Trapezoid Formula
Area of the trapezoid formula can be defined as A = ½ (a + b) h in English. Surely, it is the same in Japan but the order is different. In Japan, it can be taught A = (a + b) h ½. I have heard that we should care about teaching its order too. Thus, it can be expressed not h(a + b) but (a + b) h, though the result is the same. I wonder where the difference comes from.
Under the GIGA school project going on currently, there are many free and accessible online materials issued by Japanese BOEs. A coworker of mine suggested a nice one from Kumamoto prefecture. It is easy to use and all students enjoyed using it, including those who are in special need.
Even people who do not understand Japanese, I think, can be use this material to get concepts of areas of polygons.