A comprehensive assessment system is one in which three types of assessments: summative, benchmark, and formative assessments are routinely administered to all students in K-12 classrooms. The first part of this report summarizes the research on comprehensive assessment systems and provides clarity in terms of how each individual assessment type is defined; and the purpose of each assessment type in a comprehensive system. The second half of this report provides practical implications for districts that are considering developing comprehensive assessment systems. In summary, school administrators should have a good sense of the qualities they want in assessment systems and in individual items and, if purchasing products from a vendor, should scrutinize vendors' claims about reliability, validity, and alignment with state content standards. Finally, districts should proceed carefully when developing and deploying comprehensive assessment systems.