Research has shown that teaching mathematics through problem posing, or problem-posing based learning (P-PBL), is a student-centered instructional approach that can improve students' cognitive and affective aspects of learning. However, since textbooks continue to include very few opportunities for problem posing, researchers have been working to support teachers to integrate problem posing into classroom instruction, drawing on textbooks as a resource. In this paper, we describe how teachers in the P-PBL Project have engaged in instructional change with support from researchers around a high-quality middle school mathematics textbook series. Through curriculum analysis and cases drawn from meetings with project teachers, teacher journals, and classroom observations, we examine problem-posing tasks in textbooks and how project teachers use textbooks as a resource for P-PBL. We found that, for a given curriculum, problem posing catalyzes changes in teachers' classroom instruction, but care must be taken to connect such changes to textbook lesson learning goals. This study also shows the affordances and challenges of textbooks the teachers encountered as they learned about P-PBL. To conclude, we propose promising future directions for research based on observations stemming from our work with teachers.