abilities in large-scale assessments. First, in many cases, assessments based on IRT allow for everyone's scores to be placed on a common scale, even though different students have been given different items. Given the wide range of performance levels among students, including students with disabilities, it is unlikely that the same set of items will be appropriate for everyone. Second, IRT makes it possible to assess changes in the reliability of scores as a function of a student's skill in what the assessment is measuring. Thus it is possible to identify an assessment that may not be reliable for low-scoring students with disabilities, even though it is reliable for high-scoring students. Third, IRT provides sophisticated methods for identifying items that are biased for students with disabilities.

Computerized testing also holds promise (Bennett, 1995). One of the accommodations most often given to students with disabilities is extra time. But, as noted earlier, extra time may undermine the validity of scores. Computer-based "adaptive" assessments allow students with a wide range of skills to be tested at a reasonable level of reliability and in a shorter amount of time by adapting items individually. This makes it possible to "give more time to everyone." Computer-based adaptive tests can be shorter than traditional tests but still comply with measurement principles. The need for accommodation in test administration is reduced, thereby circumventing the validity problems.

Finally, computer-based tests may allow students with disabilities to participate in simulated hands-on assessments through adaptive input devices, such as a light pen mounted on a head strap. These can replace assessments requiring manual movements that are impossible for some students. However, as Baxter and Shavelson (1994) have shown, computerized simulations of hands-on tasks can yield results surprisingly unlike those generated by the original tasks, so this approach will require careful evaluation.

The committee's findings and recommendations about students with disabilities are reported in Chapter 12.



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