School library services (SLSs) provide curriculum resources and expertise to schools. Changes in educational policy have affected the resourcing and security of these services. This article reports on a United Kingdom Literacy Association (UKLA)-funded case study of one SLS co-designed with two librarians from the service. The aims were to investigate the role and impact of the service and to identify priorities for the development of the service. Data were collected using a mixed-methods approach, through an online survey to 226 schools (67 responses representing 43 schools received) and semi-structured interviews with teachers and senior leaders from 3 schools. Two phases of data analysis were conducted: the first was deductive coding to inform a service impact report, and the second was reflexive thematic analysis conducted independently of the partner SLS, the results of which are discussed here. The data showed that the value of SLSs should not be underestimated. The responses evidenced that services were vital to ensuring a sustainable book-rich curriculum and provided a valuable source of curriculum and literacy expertise, which supported teacher's professional development. This study indicates that the loss of SLSs in many parts of England could be of significant detriment to teachers and children and raises concerns about equality of access to books.