Researchers at the Center for the Study of Curriculum at Michigan State University have developed a tool to help teachers implement the Common Core State Standards in mathematics by letting standards, not textbooks, guide their instruction. Using the web-based Textbook Navigator/Journal, teachers can pick a standard and ask which portions of the textbook cover it, or they can use the Navigator to identify which Common Core standards are embodied in a particular lesson in the textbook. The Navigator lets teachers control their mathematics instruction, liberating them from rigidly following textbooks and allowing them to focus on teaching the content their students are expected to learn. The Navigator is based on the results of careful analyses of 34 textbook series and 185 individual mathematics textbooks.