students with disabilities have not taken part in state and district-wide assessments (National Research Council, 1999a). Although state policies vary widely, one survey found that 37 states in 1998 allowed exemptions from all assessments for students with disabilities, and another 10 allowed exemptions from some assessments for such students (Council of Chief State School Officers, 1998).
In addition, although many states have allowed students with disabilities to take the tests with accommodations and adaptations, the policies that determine which students qualify for accommodations have varied, and test results for students who are administered accommodated assessments have often been excluded from school reports.
Excluding such students from assessments and accountability is problematic. First, it sends a signal that such students do not matter, or that educators have low expectations for them, and that states and districts are not responsible for their academic progress. Second, exclusion throws into question the validity of school and district reports on performance; if such reports do not include the performance of a significant number of students, do they truly represent the level of student performance in a school or district? Third, leaving students with disabilities out of assessments deprives such students, their parents, and their teachers of the benefits of information on their progress toward standards.
Yet while including all students in assessments may be a worthwhile goal, doing so poses enormous problems. While for some students with disabilities, state and district tests yield valid and reliable information, for many others, the effects of accommodations on the meaning and validity of test results is unknown.
The population of students with disabilities is diverse. Altogether, about 10 percent of the school population is identified as having a disability. Such disabilities range from mild to severe, and include physical, sensory, behavioral, and cognitive impairments. Some 90 percent of the students who qualify for special services under the Individuals with Disabilities Education Act (IDEA) fall in the categories of either the speech or language impairment, serious emotional disturbance, mental retardation, or specific learning disability; of these, half have learning disabilities. However, the definitions of those categories vary from school district to school district and from state to state. Some have argued that the decision to classify students as having a disability may have more to do with educational policy and practices than with the students' physical or mental capabilities (National Research Council, 1997a).
Students who qualify for special education services under the IDEA are educated according to the terms of an individual education program (IEP), which is a program negotiated by the child's parents, the school, and service providers. Although evidence varies on the effectiveness of such plans, particu-