This study compares the organization and development of mathematical practices in school and work settings where design is a leading activity. In collaboration with middle school mathematics teacher/researchers, we use case methods to compare the activities of students working on design projects with those of adult practitioners in areas like architecture, population ecology, and cartography. Workplace studies overlap with a summer practicum for participating teachers. School studies are then conducted in the classrooms of these teachers, who use project-based curriculum units developed around design problems in these areas. Comparative questions are framed at three levels of analysis: 1) the construction and use of different representational systems, 2) the organization of design work around recurrent activity structures, and 3) forms of participation that shape discipline-specific identities within school and work settings. Major outcomes include: detailed studies of quantitative reasoning and modeling in design projects (four classrooms and four worksites), a comparison of how mathematical practices develop and are organized across these sites, and a collection of video cases that illustrate these studies and are available to different communities with a stake in restructuring mathematics education.The project is funded by the National Science Foundation. Rogers Hall is the principal investigator.