The standards-based reform movement has resulted in the wide-spread use of summative assessments designed to measure students' performance at specific points in time. While many have hoped that these end-of-year tests would provide constructional useful information for educators, they do not. This is not because there is something "wrong" with these summative accountability tests, rather that they were not designed to meet instructional purposes. Recognizing the inherent limitations of summative assessment, educators are looking for additional assessments to inform and track student learning during the year. Large numbers of vendors are now selling what they call "benchmark," "diagnostic," and/or "predictive" assessments with promises of improving student performance. These systems often lay claim to the research documenting the powerful effect of formative assessment on student learning. However, the research in this area, including the seminal Black and Wiliam (1998) meta-analysis, evaluated formative assessments of a very different character than essentially all current commercially-available interim assessment programs. This policy brief provides a definition to differentiate between true classroom formative assessment and the interim assessments currently in the marketplace. It also describes a framework for understanding what purposes interim assessments can serve and considering their appropriate role in a comprehensive assessment system. The goal of this brief is to help district leaders thoughtfully examine the commercially-available interim assessment products, develop strong specifications for a customized system, develop their own interim assessments, or determine that interim assessments are not an appropriate tool for their assessment system. A second goal is to help state leaders consider what role they might play in supporting effective interim assessment practices. This policy brief is organized into the following seven sections: (1) Distinguishing among Assessment Types; (2) Questions to Start With; (3) Determining the Purpose for the Interim Assessment; (4) Characteristics of an Effective Interim Assessment System to Be Used for Instructional Purposes; (5) Current Commercially Available Interim Assessment Systems; (6) Implications for District and State Decision Makers; and (7) Conclusions.