The Winsight Assessment System integrates summative, interim (including both benchmark assessments and testlets), and formative assessment components initially focused on mathematics and English language arts (ELA) in Grades 3–8 and high school. This report provides a preliminary theory of action for the Winsight Assessment System. A theory of action illustrates the claims made about a program through a logic model (a diagram that links program components to intermediate and long-term outcomes for various stakeholders) and a review of supporting literature for those claims. We first briefly describe the assessment and professional support components of the system, and then we identify 5 principles that undergird the theory of action and the logic model. We then present the logic model diagram and set of claims in the logic model that are ultimately intended to lead to improved student outcomes in the educational system. The report ends with a summary of logical, theoretical, and empirical evidence that supports these claims.