Many clients who appear for psychological assessment are found to be struggling because of physical or motor performance disabilities in addition to developmental delays or cognitive-processing disabilities. The effects of orthopedic conditions on testing have been known for decades (e.g., Briggs, 1960). Despite the attention to physical disabilities, there are few currently published studies of how developmental delays or motor performance affect performance on cognitive and achievement batteries exclusive of the studies reported in test manuals (e.g., Roid, 2003, on the Stanford-Binet Intelligence Scales, Fifth Edition, [SB-5]). Often these groups are the smallest among the validation groups.

Participants for the current study included individuals aged 3 to 18 from samples collected during the standardization of the SB-5: (a) 22 individuals with orthopedic disabilities (9 with cerebral palsy, and 13 with other motor disabilities); (b) 54 individuals with developmental delays; (c) 104 individuals with documented intellectual disabilities; and (d) 211 normative cases from a stratified random sample of the U.S. Instruments were the 10 subtests of the SB-5 (Roid, 2003). The SB-5 consists of 5 each Verbal and Nonverbal tests representing 5 cognitive factors. Performance of the 4 samples was compared on each of the SB-5 subtests.

The normative sample showed the highest level of performance on all subtests. The orthopedic cases showed higher levels of cognitive performance than the developmental delay and intellectual disability samples except on tasks requiring refined motor skills. These findings suggest that SB-5 subtests most clearly differentiate the orthopedic cases from Developmental Delay, Intellectual Disability, and Control when it involved the manipulation of forms. These included Nonverbal Visual-Spatial, involving the placement of pieces in a formboard or form completion using tanagram-style pieces, and the Nonverbal Working Memory, involving the tapping of blocks. Because response speed is scored for these subtests, it is concluded that standardized test procedures are biased against those whose motor skills are impaired.

The separation of speed from cognitive ability is crucial for the fair assessment of cognitive abilities among individuals with physical disabilities (Braden & Elliott, 2003). Appropriate accommodations are needed to fairly assess cognitive functioning for individuals with orthopedic disabilities.