When in-service teachers (IST) did not know how to implement mathematics problem posing (MPP) into teaching one concern was the lack of tasks. When prospective elementary teachers (PET) were asked to imagine how students posed problems they could not as they did not teach yet. This paper reports how a math teacher educator (MTE) implements MPP into teacher education and bridge IST and PET under a curricular reform in Taiwan. She started with the provision of six types of MPP tasks, given in four math strands, adding to a total of 52 MPP tasks. While the teacher educator shared knowledge on MPP tasks, teachers shared results on task use and students’ outcomes. The returned students’ outcomes were used in prospective teacher training; and, the analysis of data-handling tasks was reported as examples. Prospective teachers experienced what students posed and judged the math knowledge students possessed. Collaborative actions in studying MPP tasks and students’ outcomes provide professional development for all teachers (MTE, IST, and PET).