Up to 1.0% of the total tested state student population in a subject area may participate in the alternate assessment based on alternate academic achievement standards (AA-AAAS). This Brief presents the results of analyses of states' AA-AAAS participation rates from 2015-16 through 2018-19. Information is presented on: (a) the number of states meeting the 1.0% participation requirement in each year from 2015-16 through 2018-19 for mathematics (i.e., math) and reading/language arts (i.e., reading), and (b) states with decreasing and states with increasing patterns of participation rates across the four years in math and reading.