This chapter presents the evidence on the size and nature of the rich/poor reading achievement gap. It evaluates the evidence on factors, such as teacher quality and summer reading activity, that contribute to the achievement gap. The chapter discusses the evidence on summer reading loss as well as the evidence that summer reading loss is primarily attributable to the limited access to books that poor children are likely to experience every summer. In a classic study of summer reading loss, Heyns documented the rich/poor reading achievement gap in the Atlanta schools nearly forty years ago. She reported that children from middle-class families generally gained more reading proficiency during the summer than children from low-income families. In fact, this latter group actually lost reading proficiency during the summer months. However, academic growth during the school year was roughly comparable for both groups. It was during the summer months that poor students lagged behind their financially better-off peers.