This resource is part of a series of reports about challenges facing statewide science assessments and innovative solutions states are enacting to meet those challenges. Deciding to implement a system of assessments is a critical step toward ensuring that all students are getting the high-quality science education they need--but it is also challenging terrain to navigate with several trade-offs and decisions to consider. This guide is designed to help state leaders--including science supervisors, assessment directors, and chief academic officers--design effective and strategic systems of assessment in science. This guide walks through five iterative steps all decisionmakers should consider when deciding on the nature and scope of their systems. For an analysis of how other states are currently approaching systems of assessments and state examples, please see the other resources in this series.