Data can be a powerful tool for self-evaluation, goal setting, and advocacy in the school library. Regardless of the grade level or the size of the student body, any school library has meaningful data to mine and learn from. Basic data such as circulation numbers can impact a myriad of areas relevant to student learning such as collection development, reading-engagement plans, and book-promotion activities. For those unequipped to analyze and interpret data, the vast options can be overwhelming. However, to abandon data, or to skim numbers while not understanding or acting upon them, does a disservice. As school librarians look for ways to prove relevance and effectiveness, and as they continue to champion best practices, innovation, and student impact, data becomes a catalyst for change and a support for sustainability in turbulent times. This article discusses the best practices in preparing for library/librarian data evaluation.