Under IDEA, if testing is used, several instruments and procedures must be used to eliminate bias and to gather information about the student. These procedures must be research based.
In the past, 2 standard deviations was the measure used if the discrepancy model is used. However, some states, knowing this is not an exact and that kids below this may need help too, make their cut off less. BTW, the discrepancy model is no longer included in the definition in IDEA 2004 for a specific learning disability (SLD). They encourage the use of response to intervention and research based practices for identification. However, how an adult is diagnosed would be different, since an adult is not under IDEA any more, but under ADA and 504
You might search the California department of education web site for their rules on adults. You may also check out the US goverment department of education site and look up 504 and Americans with Disabilities Act.
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