In recent years, many states have adopted policies to ensure students are reading proficiently by third grade. This kind of policy transfer across states is not a unique phenomenon; researchers have documented analogous proliferations of similar policies both in and outside the field of education. However, there has been little attention paid to how policy transfer happens in K-12 education policy, particularly at the state level. To better understand how education policies spread across states, we turn to the case of Michigan's Read by Grade Three Law, which was adopted in 2016. Guided by the Multiple Streams Framework and the theory of policy transfer, we trace the policy process surrounding the Law's conception, development, and passage, relying on data from semi-structured interviews from 24 stakeholders involved in the development of the Law and supported by policy documents from all 50 states and D.C. We find that events in the problem and political streams opened a policy window that allowed for the passage of the Law. These findings contribute to policymakers' and other stakeholders' understandings of the development and passage of third-grade literacy policies--information that will be important as these policies continue to receive national attention in both the policy and research communities. Moreover, this study is one of few to focus on the critical role of policy entrepreneurs in joining together the multiple streams, while also providing a nuanced view of how policy transfer and policy entrepreneurship promote the convergence of ideas and solutions to particular problems. [For the corresponding grantee submission, see ED620198.]