This month’s blog post comes from guest contributor Dr. Scott Hamilton, a licensed clinical psychologist at Understanding Minds in Atlanta, GA. We asked Dr. Hamilton to explain the “discrepancy approach” to diagnosing Learning Differences and why many organizations will no longer accept that methodology when applying for accommodations.
For many years, the “discrepancy approach” had been the gold standard in the diagnosis of learning disabilities. This approach typically involves comparing a student’s academic achievement to their cognitive abilities (i.e., “IQ”), with the theory that a significant gap between the two indicates the presence of a learning disability. However, this method presents several shortcomings, leaving it an unsound basis for diagnosis. In fact, many states (including Georgia) no longer allow the discrepancy approach in the identification of learning disabilities in public schools.
There are myriad reasons why the discrepancy approach is unsound. For one, the discrepancy approach relies heavily on standardized testing. Standardized tests may not accurately reflect a student’s true abilities or potential due to various factors including test anxiety, cultural bias, and socioeconomic disparities. Many students who struggle academically do not have a corresponding low IQ score, which means they may be overlooked for necessary interventions despite facing significant barriers to learning.
Secondly, imagine a scenario where Student A with a 130 Full Scale IQ has reading scores around 95 (the 37th percentile). This is more than a two-standard deviation “discrepancy” under the old ways, which may have been flagged as signs of a learning disability. The reality is that Student A’s reading score is still normatively average. Now, take Student B, with a full-scale IQ of 92 (30th percentile), but reading scores
around 82 (12th percentile). This may not have been seen as a severe enough “discrepancy” to qualify as a student with a learning disability. But which student truly needs the resources more? Under the old system, there was the potential that Student B would be denied, and Student A would receive services.
Additionally, the discrepancy model fails to account for the dynamic nature of learning and development. Learning disabilities can manifest differently depending on the context and the specific skills being measured. A student may exhibit strengths in certain areas while struggling in others, and a static comparison of IQ and achievement does not capture these nuances. A rigid classification can lead to misdiagnosis and inappropriate educational placements, depriving students of the tailored support they need.
More troubling, relying on cut-off scores to determine eligibility for services can be arbitrary and exclusionary. For instance, a student who scores just below the threshold may be denied the help they require, while another student with a similar level of need but a slightly lower discrepancy might receive support. This creates an inequitable system that does not address the individualized nature of learning challenges.
While the discrepancy approach has been a traditional method for diagnosing learning disabilities, it has notable limitations. Neuroscience would tell us that students need comprehensive and holistic assessment strategies. The movement in recent years has been towards consideration of multiple factors, such as performance in the classroom, teacher observations, and a profile analysis of a student’s strengths and challenges.
Using a holistic approach that considers multiple factors will result in more accurate diagnoses and better educational outcomes for students facing learning challenges. If you see a psychoeducational assessment that talks about “discrepancy” between cognitive abilities and academic achievement scores, you should immediately question that psychologist’s knowledge and experience with the latest methods to identify learning disorders.
Dr. Scott Hamilton
scott@understandingmindsatl.com