Statistical literacy is a skill that will be required by all students, but only limited insights exist into how it can be developed in middle schools. Research is required that identifies design principles and provides didactic materials for developing statistical literacy in actual middle school classrooms, meaning classrooms in which statistics is only seen as a small part of mathematics. This study conceptualizes statistical literacy as not only the ability to read given statistical information, but also as the ability to imagine the often unreported data and underlying assumptions of this information. This allows the Design Research study to identify design principles for developing statistical literacy in which students actively engage with conflicting statistical information about the same data. The working mechanisms of the design principles are illustrated through didactic materials, and student responses show how the design principles can be used to develop statistical literacy in middle schools.