commodations on test performance and on the inferences based on test results are not clearly understood. Findings from research are not conclusive with regard to the comparability of inferences based on scores obtained under accommodated and nonaccommodated conditions (National Research Council, 2004). Nevertheless, states are expected to include test results for students with disabilities and English language learners in their aggregated reports and to report disaggregated group results for these students, and they may be held accountable for demonstrating that these students are making progress in science.
A principle known as universal design, which was developed by architects and other designers, has been adapted to educational measurement and holds some promise for ameliorating some of the difficulties that testing accommodations present. The principle is that products and buildings—or assessments—should be designed so that the greatest number of people can use them without the need for modification—that is, to eliminate unnecessary obstacles to access. In the case of assessment this might mean, for example, that if all students had more than enough time to complete an assessment task, offering extra time to students who need it because of cognitive disabilities would not provide them with an unfair advantage over other students. The application of universal design principles to assessment has not, however, been fully developed; the committee hopes that with further research it will provide valuable alternatives for states. Further information on this topic is available from the National Center on Educational Outcomes (http://education.umn.edu/NCEO).
Although the research base on the effects of accommodations on the interpretation of test scores and the inferences that can be supported by results is inconclusive, some guidance can be offered for those making decisions about test development and the provision of accommodations. First, states and their test developers should make clear which inferences are to be based on test results. Clear specification of the target skills evaluated and of the ancillary skills required to demonstrate proficiency on the target skills can improve decision making about accommodations. For example, in a written science assessment with open-ended responses, is writing a target skill or an ancillary skill? Is the assessment designed to make inferences about science knowledge, about written expression of science knowledge, or about written expression of science knowledge in English? The answers to these questions can assist with decisions about accommodations, such as whether to provide a scribe to write answers or to provide a translator to translate answers into English. If mathematics is required to complete the assessment tasks, is mathematics computation a target skill or an ancillary skill? Is the desired inference about knowing the correct equation to use or about performing the calculations? (Here, the answers can guide decisions about use of a calculator.) Further discussion about identifying target and ancillary skills and about