Participating in an evidence-based practice workshop in 2005 was a transforming experience for the author. She realized that the traditional statistics that she had painstakingly gathered and recorded for her annual report did not provide evidence of actual learning. Evidence acquired through assessment, both formative and summative, provides the evidence that "school libraries are more than repositories of information or alternatives to study halls--school libraries are places of essential learning for every student in the school." So five years later what kind of evidence about the school library program's effect on learner achievement can the author give to the school board or to the local newspaper? Rather than statistics on the number of books circulated, number of classes in the library, number of teacher collaborations, number of students from study halls, the author provides data on a variety of measures related to information literacy and research skills. In this article, the author shares how her class builds and triangulates evidence of library success in a different perspective. This research-derived evidence helps teacher librarians shape and direct what they do as they work with students one-on-one and in groups and how they design and implement their collaborative lessons with teachers. (Contains 2 tables.)