State education agencies are now required to report on the educational performance and progress of all students, including students with disabilities. States are beginning to report trends, and to compare trends in performance of students with and without disabilities. We compare the effects of different methods of analyzing trends to illustrate how failure to account for changes in classification of students will lead to misinterpretation of data on the performance and progress of students with disabilities, and inappropriate policy decisions. We compare three ways of looking at trends over time, and use data from 5 years of assessment in a large state to illustrate the effects of students who change classification. We discuss how accounting for changes in classification of individual students will lead to more appropriate decisions and help avoid negative consequences for students with disabilities.