In recent assessments, the National Center for Education Statistics (NCES) has permitted schools to exclude some students with disabilities or limited English proficiency because it believed that its assessments would not accurately measure the ability and achievement levels of these students. The exclusion of a portion of students from assessments by the NCES has raised doubts about the validity of its data. This report discusses the data validity concerns related to the current policy and explains how the NCES assesses and surveys students with disabilities and limited English proficiency. Approximately 7% of students with disabilities attend special schools and thus are not assessed by the NCES. However, about 50% of students with disabilities are currently assessed. Alternative ways to collect outcome data on students with disabilities who are currently excluded include making accommodations to the NCES assessment procedure by, for example, providing additional time to complete the test or providing a separate room in which to take the test; conducting portfolio assessments; and collecting background data from the schools about students' achievement and abilities. The 1995 field test of the National Assessment of Educational Progress will examine new procedures for assessing students with disabilities or with limited English proficiency. (Contains 12 references.) (SLD)