The American Association of School Librarians' (AASL) Causality: School Libraries and Student Success II (CLASS II) project was the first step in developing a long-term, three-phase school library research agenda to investigate causal relationships between school libraries staffed by professionally prepared school librarians and student learning. This report, designed for school library researchers and practitioners, features: (1) an executive summary of the CLASS II objectives and research process; (2) an overview of select research findings as they relate to the Shared Foundations from AASL's National School Library Standards for Learners, School Librarians, and School Libraries (2018); and (3) recommendations for future research directions. [For the full report, see ED624354.]