In Situation A "Formulating a problem mathematically,"teachers show students the original situations or problems, and students try to formulate them as mathematical problems in response to their own learning experience. In Situation B "Investigating various approach to the formulated problem,"students are expected to find their own solutions on the basis of their experience.Teachers direct students to discuss the relations of wide variety of solutions proposed, and lead them to integrate seemingly unrelated solutions into a more sophisticated one. In Situation C "Posing advanced problems,"students try to pose more general problems on the basis of their activities in Situation B. Through solving these problems, they are expected to find more general solutions.