The paper describes the history of how learning trajectories (LTs) were associated with the Common Core State Standards for Mathematics (CCSS-M) and discusses the degree to which the two correspond faithfully. It reports on a website, www.turnonccmath.com, which organizes the K-8 standards into 18 LTs describing the development of big ideas over time, informed by empirical studies of learners. The paper illustrates how descriptors for each LT identify: (1) conceptual principles, (2) strategies representations, and misconceptions, (3) meaningful distinctions and multiple models, (4) coherent structure, and (5) bridging standards. The design principles for the website are illustrated describing how the CCSS-M are related to a learning trajectory on division and multiplication. [For the complete proceedings, see ED584829.]