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By Kim Glenchur
The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) provides diagnostic guidelines for determining the presence of a learning disorder, but each state has its own set of rules for establishing the presence of a learning disability based on IDEA (Individuals with Disabilities Education Act). Many definitions use the concept of discrepancy, an underachievement difference between actual performance and expected performance in a child, given her or his intelligence, home environment, and school attendance, among other factors. A discrepancy of two or more standard deviations (of actual language or math performance below that expected for a given intelligence level) is considered significant, and is one way to qualify a student for special education. If the discrepancy is between one and two standard deviations, then other factors may be considered such as cognitive problems affecting intelligence testing, an emotional disorder like depression, a general medical problem, or cultural background. Conversely, if a sensory deficit exists, then the discrepancy must be greater than normally found in people with that same deficit.3
Laws have differentiated disability from disorder. IDEA neither states which evaluation measures are to be used in the identification process, nor clarifies what threshold levels determine the presence of a disorder or a disability.
Until the recent promise of medical imaging, medical diagnostic tests for LD have proven inadequate over the last century. Thus psychological tests, however flawed in inferring neurological problems, have been the best set of tools available to assess learning performance. Nevertheless, psychological tests are statistical instruments, and using statistical concepts has become accepted practice in fulfilling the law. According to Section 504, a learning disorder becomes a disability when learning performance is "substantially" limited. It is easy to understand, then, how substantially limited has become equivalent to statistically significant. Thus, disability — and therefore eligibility — have been defined as pertaining to those performing two standard deviations away from the mean, or the bottom 2-½%. Some school district definitions set the disability threshold at the bottom 5%, the same total figure of those who would lie either significantly below or above the mean. Thus, numbers have come to define disability.
Be wary of population figures that say that about 2%-5% of the school population has a certain type of learning disability, because disability may have been defined as being the bottom 2%-5% in the first place. This is the reason for the dissatisfaction in the identification process. Indeed, Sally Shaywitz has found the incidence of reading disorders approaching 20% in her Connecticut longitudinal study4, and Ruth Shalev acknowledged that her 5% cutoff underestimates the incidence of dyscalculia especially given that children initially scoring in the bottom 20% continued to perform poorly.5 (You can wonder what would happen if cancer treatments were available to only the worst 2%-5% of the population — depending on the local rules governing eligibility — and in which pessimistic professionals offered little help or hope because recovery seldom occurred.)
Children whose everyday school performance is not failing enough to flag a referral for an evaluation, for whatever reason — nightly tutoring by well-educated or sacrificing parents, extraordinary effort on the part of the child, environmental deprivations precluding any possibility of an unexpected discrepancy, or extreme giftedness compensating for the disorder — will probably not be regarded as falling below a 5% threshold.
Reprinted with permission from Kim Glenchur. All rights reserved.
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