Growth-based approaches to federal accountability are receiving considerable attention because they have the potential to reward schools and teachers for improving student performance over time by measuring student progress at all levels of the performance spectrum, including progress by students who have not reached proficiency on state accountability assessments. The use of growth in accountability holds promise for students with disabilities, but measuring changes over time in academic performance with large-scale annual assessments is complex. The authors discuss practical challenges in measuring and modeling growth for students with disabilities. In addition, they identify and describe three areas in need of research on the measurement of growth: the impact of testing accommodations, the impact of test difficulty, and the longitudinal characteristics of the population of students with disabilities. (Contains 1 figure, 3 tables and 2 notes.)