With the reauthorization of the Elementary and Secondary Education Act (ESEA) in 2015, renewed attention was paid to the importance of guidelines for participation in alternate assessments based on alternate achievement standards (AA-AAS) and to understanding of who the students are who have significant cognitive disabilities. The analyses presented in this report were conducted to highlight the alternate assessment participation guidelines and definitions of students with the most significant cognitive disabilities that were in place just prior to the start of the 2017-18 school year. Specifically, the report documents the status of states' participation guidelines and definitions as of August, 2017. The analysis includes the factors that states indicated should and should not be considered when making decisions about participation in the AA-AAS. It also documents the format of the guidelines that states made available to decision makers. Finally, it examines the extent to which states provided an explicit definition of "students with the most significant cognitive disabilities."