The purpose of this study was to understand how Anna, a class teacher, applied problem posing to a grade three classroom setting, identified teaching problems, and resolved them. The action research was conducted for one whole semester in the mathematics class of the third grade. Data included videos, observation notes, interviews, reflection notes, and, activity sheets. The action researcher underwent three waves: The Groping stage, the Transition stage, and, the Mature stage. Students gradually learned MPP successfully. Examples of mensuration and shapes on students’ outcomes were reported. Through evaluating attempts in MPP, Anna completed this action research voyage and witnessed her growth.