Differentiation is an important practice in today's increasingly diverse classrooms. The researchers used collective case study methods to investigate the role of the principal in supporting differentiated literacy instruction in three purposively selected elementary schools with a documented history of literacy differentiation. For the fourth and fifth grade teachers (n = 15) and their principals (n = 3), differentiated literacy instruction was synonymous with guided reading. To facilitate this practice, principals protected the 60-minute literacy block from push-in or pull-out services and leveraged the expertise of district staff. The principals also supported guided reading by providing teachers with structured opportunities to collaborate, where teachers shared resources, narratives, and expertise. Additionally, the principals purchased texts beyond the district curriculum, strategically networked teachers, and evaluated teachers during their literacy block, when teachers were expected to differentiate their instruction.