In this study, we explored elementary school teachers’ experiences working on open-ended mathematics tasks during a 10-day professional development (PD) workshop. Teachers engaged with the tasks daily in a session call Morning Math (MM). Thirty-two elementary teachers from three school districts in the USA participated in a 2-year professional development (PD) program. Analysis of videos of teacher engagement in the tasks and interviews shows that the use of open-ended mathematics tasks embedded within problem-solving focused PD could shape elementary school teachers’ personal meanings about learning mathematics through problem-solving. The findings indicate that the teachers’ take-aways from the PD were not limited to the mathematical content of the MM problems (i.e., mathematical residue), instead teachers’ experiences with open-ended mathematics tasks engendered personal meanings reflecting pedagogical residue with cognitive, affective, and social components. This result shows the crucial role of PD in shaping teachers’ mathematics-related personal meanings which research suggests that it will subsequently influence their beliefs and instruction.