According to one report, when schools have high-quality library programs and librarians who share their expertise with the entire school community, student achievement gets a boost. This report discusses multiple studies that emphasize the importance of librarians, and how they are associated with better student outcomes. It is stated in this report that multiple studies have found that test scores tend to be higher in schools where librarians have an active role in where administrators, teachers, and librarians themselves think of the school librarian as a school leader, co-contributor, and instructional planner to the administration and educational curriculum of the school.
Lance, K. C., & Kachel, D. E. (2018). Why school librarians matter: What years of research tell us. Phi Delta Kappan, 99 (7), 15-20. http://www.kappanonline.org/lance-kachel-school-librarians-matter-years-research/