School librarians have always been teachers, even before the term "teacher-librarian" was coined. They teach every time they help students select books, locate and evaluate resources for research projects, or troubleshoot a computer problem. When they assist students, they explain and model the steps they are taking. Teaching for school librarians is a continuous, fluid process, dictated by the specific needs of individuals. To be consistent and efficient they teach whole class library lessons to reach all their students. Teaching requires assessment, however, which has always been a challenge in the library. Library assessments should be authentic assessments where students demonstrate their understanding of skills, yet the logistics of constructing, administering, and correcting them can be daunting. Performance assessments generally take longer to administer than worksheets, and time is a luxury in the library. Library schedules often prevent a lesson from spilling over into the next day. Both lesson and assessment must be completed in one class period or less. But by the time the classroom teacher takes attendance, focuses the students, leads them down the hall, and settles them into the library, the author is often left with 30 minutes (or less) for a lesson and checkout time. She feels rushed to teach the lesson, and even more rushed to have the students complete it. There is no time to allow for differentiation or to assist struggling students, or to accurately measure 30 individual performances. And when the library lesson is over, there is no accountability of what the students did or did not understand. In this article, the author describes a system that could quickly teach--and assess--each library skill to every student in the allotted time. (Contains 1 figure.)