MONSAKUN is a software of learning by problem-posing for arithmetic unit word problems. In this paper, results of an experimental use of MONSAKUN of addition and subtraction in all grades and classes in a public elementary school are reported. The contributions of this report are (1) successful use of MONSAKUN for addition and subtraction in all grades and classes in a public elementary school, and (2) obtaining data suggesting use value in upper grades classes. Although MONSAKUN has been used in a few elementary schools so far, its use was for part of grades or classes in the schools. Because the use of MONSAKUN in all grades and classes in a public elementary school is the first case, this report is novel and useful for developing practice of MONSAKUN. Regarding (2), previous studies have mentioned that the arithmetic unit word problems of addition and subtraction are mastered by the third grade. The result of this use shows that problem posing of the arithmetic unit word problems of addition and subtraction is not easy even 5th or 6th grade students. It suggests that some of the students in 5th or 6th grade don’t have enough “relational understanding” that required in problem-posing in MONSAKUN although they have enough “instructional understanding” that required in problem-solving tests. As the next step of this experimental use, we plan to use MONSAKUN in usual classes in the same school.
