http://ime.math.arizona.edu/progressions/The Common Core State Standards in mathematics were built on progressions: narrative documents describing the progression of a topic across a number of grade levels, informed both by research on children's cognitive development and by the logical structure of mathematics. These documents were spliced together and then sliced into grade level standards. From that point on the work focused on refining and revising the grade level standards. The early drafts of the progressions documents no longer correspond to the current state of the standards.It is important to produce up-to-date versions of the progressions documents. They can explain why standards are sequenced the way they are, point out cognitive difficulties and pedagogical solutions, and give more detail on particularly knotty areas of the mathematics. This would be useful in teacher preparation and professional development, organizing curriculum, and writing textbooks. Progressions documents also provide a transmission mechanism between mathematics education research and standards. Research about learning progressions produces knowledge which can be transmitted through the progressions document to the standards revision process; questions and demands on standards writing can be transmitted back the other way into research questions.This project is organizing the writing of final versions of the progressions documents for the K–12 Common Core State Standards. The work will be undertaken by members of the original work team of the progressions and also by mathematicians and educators not involved in the initial writing.