Standards have been at the heart of state and federal efforts to improve education for several decades. Most recently, standards-based reforms have evolved with a focus on more ambitious "college- and career-ready" (CCR) standards. This paper synthesizes the results of a seven-year national research center focused on the implementation and effects of CCR standards. The paper draws on evidence from a quasi-experimental longitudinal study using NAEP data, a cluster-randomized trial of an alignment feedback intervention, and detailed implementation data from state-representative surveys and case studies of five districts. Situating our work in a "policy attributes theory," we find important gaps in the theory of change underlying current standards-based reform efforts. We conclude that the CCR standards movement is not succeeding in achieving its desired outcomes. We make specific suggestions for improving instructional policy, including (a) providing more specific instructional guidance, (b) reconceptualizing professional learning, (c) building buy-in through the involvement of trusted leaders, (d) providing better supports for differentiation, and (e) devoting attention and guidance to the intersection of content and pedagogy, and (f) addressing persistent deficit thinking among educators.