This report examines the relationship between various characteristics of students with disabilities and the probability that they would participate in the NAEP assessments, given the current methods of accommodation adopted by their state. The report describes the methodological approach which calculates for each state an expected inclusion rate based on (a) its previous inclusion rates, (b) changes in the distribution of types of students with disabilities in the state, and (c) the set of accommodations offered by the state on its own tests. The method developed is applied to measuring changes from 2005 to 2007 for grades 4 and 8 mathematics and reading assessments. The study finds that, between 2005 and 2007, in about one-third of the states there were significant changes in inclusion rates for the mathematics assessments, and in about one-half of the states there were significant changes in inclusion rates in the reading assessments. Overall, more states had, after adjusting for differences in SD populations, lower inclusion rates than higher inclusion rates of students with disabilities on NAEP in 2007 than 2005 except in grade 4 mathematics, where the numbers were about the same from 2005 to 2007. This report is the first in a series of reports that explore methodologies to measure state-level changes in inclusion rates of students with disabilities as well as English language learners (ELLs). This report focuses on the inclusion of students with disabilities who are not English language learners. (Contains 44 tables and 4 figures.)