In learning fractions and decimals, students often apply rules in whole number operations which may lead to mistakes. In this study, the investigators implemented mathematical problem posing (MPP) instruction on fractions (one fifth-grade class) and decimals (one sixth-grade class), using the sequence “Solve-Pose-Solve”. The investigators collected data including MPP worksheets, students’ diaries, teacher’s journals, and related artifacts of the lessons. Examples of the implementation of the addition and subtraction of two numbers (fractions, decimals) were reported. First, students made progress in problem posing and problem solving and behaved positively in multiple measures. Second, there were improvements in the affective and cognitive aspects of students’ learning. Third, the teachers reflected upon practice and provided tips on task design for the learning of fractions and decimals.