Numerous state impact studies show that school libraries improve student achievement and standardized test scores, yet that fact is insufficient to keep financially strapped districts from closing their libraries. Teacher-librarians must be proactive and gather data at the school-site level to demonstrate how valuable they are to students and staff. Thorough library assessments--which include daily usage statistics, community and collection analyses, and student and faculty surveys--must be performed by teacher-librarians. In this article, the author shares how she tackled new library assessment when she was still a beginning teacher-librarian.