This paper traces school library policy formulation and implementation as factors for attaining best practices in Nigerian school libraries from the inception of the National Policy on Education (NPE) in 1977 to the present. Nigeria’s post-independence educational policy advocates an active, learner-centered and resource-based constructivist approach that demands a central role for school libraries as learning and resource centers. The Policy also makes favorable mention of provision for school libraries. However, putting policy into practice has proved difficult in the almost 40 years that have followed. Since 1977 implementation has been attempted through a number of initiatives aimed at developing school libraries as a way of realizing the NPE vision. At the same time, there have been policies that proved to be detrimental to development. This paper traces policy and its implementation through the past four decades, beginning with the efforts of the Nigerian School Library Association to work with government in implementing NPE provisions on school libraries and the successful advocacy of school libraries by the Anambra State School Libraries Association and Bendel State Library Board at state level during the 1970s and 1980s. It continues by reviewing federal government programmes to improve primary education and school libraries through the National Primary Education Commission in 1989-1991 and the Universal Basic Education Commission from 1999 onwards. Policies concerned include those on provision of material resources and funding; those related to human resources, their training and position; and policies enabling use of school libraries as “the heart” of any education system.