Bias towards individuals with disabilities, such as ADHD or cerebral palsy, can result in the mislabeling of these individuals as being language impaired or intellectually disabled.  The examiner may exhibit bias against those with these disabilities for several reasons. 

First, it is difficult to determine which domain (e.g., memory, language, intellect) may be causing concern. Perhaps a child’s cognitive skills are within normal limits, but attention issues prevent him from attending to information long enough to learn it. Alternatively, when a motor disability is present, structural limitations might be affecting the individual’s ability to demonstrate cognitive and learning ability. In cases such as these, the examiner may assume that the individual has an intellectual or language disability or that their disability is more severe than it actually is. Only a thorough evaluation which is not biased against a child with attention difficulties or motor difficulties will determine the true cause of the child’s academic difficulties. Otherwise,  the child may be wrongfully placed in a very restrictive setting due to perceived cognitive limitations where the curriculum is often less rigorous and there are lowered expectations for the child’s academic success (Harry & Klingner, 2006).
As with other types of bias, there can be significant bias towards individuals with other disabilities present in commercially available testing materials. The American Speech-Language Hearing Associaiton prohibits the identification of a specific learning disorder if failure to meet grade level expectations is primarily the result of a motor disability. However,  no currently available standardized test is normed on a population in which individuals with these types of disabilities are sufficiently represented in the normative sample. Aside from bias caused by the standardization of testing materials, the test items themselves are often biased against individuals with other disabilities. Some test items may require pointing, verbalizing or the ability to keep one’s head and eyes still for long periods of time. This would prevent an individual with a serious motor disability from performing well on the test.Other items require that the individual hold lots of information in memory for long periods of time in order to repeat them or answer questions. The fact that an individual can not perform this task may not mean he or she has a language disorder or intellectual disability. Instead, he or she may have memory and/or attentional limitations that prevent him or her from performing well on these test items. Due to the bias inherent in these tests scores, standardized tests should not be used to diagnose the presence of a language disorder in these individuals.
Harry, B. & Klingner, J., (2006). Why are so many minority students in special education?: Understanding race and disability in schools. New York: Teachers College Press, Columbia University.