Students with severe and low-incidence disabilities comprise a heterogeneous population that often presents a challenge to the professionals charged with evaluating their skills and abilities. This is especially true in conducting a valid assessment of the cognitive ability of these children. Often, school psychologists are limited to the use of published norm-referenced tests (Fagan & Wise, 2000) that provide limited meaningful information to be used for educational and treatment planning and programming (President's Commission on excellence in Special Education, 2002). While these assessments can produce a comprehensive picture of intellectual functioning for most typically developing children, it is much more difficult to obtain a valid picture of overall cognitive functioning and to delineate relative strengths and weaknesses for children with severe and low-incidence disabilities. Utilizing commonly used cognitive assessment tools with these students may not provide meaningful data that can be used for educational planning and programming. It is extremely important that the assessment tools are appropriate to the population because the information related to cognitive skills is vital in educational planning and a significant component of treatment evaluation (Delmolino, 2006). This article provides a review of the literature examining a variety of tests of cognitive ability that can be used with students with severe and low-incidence disabilities. Recommendations for assessment practices for a range of specific low-incidence disabilities are described.
Nearly all standardized assessments of cognitive functioning assess a broad array of skills, including those in the visual, linguistic, and motor domains, in order to produce a comprehensive picture of intellectual functioning. As a result, individuals who take these tests need to have adequate vision, hearing, language functioning, and visualmotor skills (Sattler, 2008). For instance, one of the most widely used assessments of general intellectual ability in children, the Wechsler Intelligence Scale for Children, 4th Edition (WISC-IV; Wechsler, 2003), requires children to hear, understand directions, andto have adequate vision and fine motor skills for standardized administration (Sattler & Dumont, 2004). If a child is deficient in one of these requisite skills, Sattler and Dumont (2004) suggest either excluding subtests that rely heavily on a particular modality from the Index Score and Full Scale IQ computations, or engaging in a series of modifications (e.g., nodding to select a particular symbol instead of drawing it in Symbol Search) to make the subtests accessible. Roid (2003b) also notes the importance of adjusting cognitive assessments to accommodate examinees with disabilities in order to ensure that tests scores are indeed valid indicators of an examinee's cognitive abilities. However, little research has been conducted that examines the impact of these adaptations on the reliability and validity of the test scores. Consequently, examiners need to be cautious when interpreting results of tests that have not been administered in the manner in which they have been standardized.
Children with significant motor, visual, hearing, or linguistic limitations are unable to be comprehensively and accurately assessed utilizing the WISC-IV and most other widely used cognitive assessments. The result is that a significant number of children with severe physical, communicative, or sensory impairments are currently assessed in ways that may underestimate their abilities, perhaps resulting in inappropriate educational placements (Driver & Warschausky, 2010). Such practices are not only a severe disservice to these children, but are also in violation of federal law, which states that:
Assessments are selected and administered so as best to ensure that if an assessment is administered to a child with impaired sensory, manual, or speaking skills, the assessment results accurately reflect the child's aptitude or achievement level . …