Longitudinally modeling the growth of students with significant cognitive disabilities (SWSCDs) on alternate assessments based on alternate achievement standards (AA-AAS) presents many challenges for states. The number of students in Grades 3-8 who remain in a cohort group varies over time, depending on the methods used to construct the longitudinal cohorts. The accuracy of inferences made about student growth from such longitudinal models is further complicated when general assessments are not equated with AA-AAS which is usually the case. Measuring the growth of students switching test types is thus problematic. States must determine their priorities: measuring the growth of only AA-AAS scores that count towards making Adequate Yearly Progress under the No Child Left Behind Act (2001) or providing a more detailed look at the growth of SWSCDs over time.