Historically, how did the discrepancy model identify learning disabilities?

• A. Measuring Reading Speed
• B. Using Teacher Ratings
• C. Checking IQ Alone
• D. A Difference of Two Standard Deviations Between Achievement and Intelligence

Answer: (D)

The key idea here is using a discrepancy between what a student is capable of (as shown by intelligence testing) and what they actually achieve (as shown by achievement tests) to identify a learning disability. Historically, diagnosticians looked for a sizable gap between IQ and academic performance. If a student had relatively high cognitive ability but much poorer achievement in reading, math, or writing, that gap suggested a specific learning disability rather than a general problem with intelligence or motivation. The gap was often considered large enough when it reached roughly one-and-a-half to two standard deviations, depending on the norms used.

This approach requires both an intelligence test and an achievement test, because relying on IQ alone cannot indicate a LD—many students with high IQ don’t struggle academically, and many with low IQ may perform poorly for reasons unrelated to a specific learning disability. Conversely, measuring only reading speed or relying on teacher ratings misses the crucial comparison between expected performance (based on cognitive ability) and actual performance. The discrepancy model.

Over time, limitations of this method led to shifts toward alternative identification methods, such as RTI, but understanding this model helps explain why LD was once defined as a significant gap between achievement and intelligence.