This article used several data sets from a large-scale state testing program to examine the feasibility of combining general and modified assessment items in computerized adaptive testing (CAT) for different groups of students. Results suggested that several of the assumptions made when employing this type of mixed-item CAT may not be met for students with disabilities that have typically taken alternate assessments based on modified achievement standards (AA-MAS). A simulation study indicated that the abilities of AA-MAS students can be underestimated or overestimated by the mixed-item CAT, depending on students' location on the underlying ability scale. These findings held across grade levels and test lengths. The mixed-item CAT appeared to function well for non-AA-MAS students.