Learning Disabilities - The Discrepancy Issue

The "discrepancy issue" has been established as the primary criterion for identifying children with LDs. Unfortunately, discrepancy formulae are controversial, potentially inaccurate, and inappropriate for detecting cognitive deficits. There are three types of discrepancy formulae.

With an aptitude-achievement discrepancy, a disparity exists between a child's intellectual ability (as measured by an intelligence test) and his actual level of academic achievement (measured by an achievement test). Certain LDs (e.g., a short-term memory problem or central processing dysfunction), however, may also affect a child's performance on IQ tests, thereby reducing the discrepancy between aptitude and achievement. This discrepancy model is useful from third grade onward, and certain disabilities (such as fine motor dyspraxia, retrieval memory dys-function, and organization problems) often are not detected. Children with the most severe LDs frequently have the smallest discrepancy.

An intracognitive discrepancy (a disturbance in basic psychologic processes) occurs in children who have a specific type of cognitive dysfunction such as a deficit in auditory processing, short-term memory, or visual processing. This type of LD is difficult to operationalize, but is useful in identifying preschool and primary-age children who have learning problems.

An intra-achievement discrepancy reflects divergence or inconsistency in educational achievement performances. This could occur between academic areas (such as reading versus mathematics) or within an academic area (such as a marked difference between reading decoding and reading comprehension).

Regression models, which attempt to correct the problems inherent in discrepancy comparisons, are used in many states. Here a statistical relationship between IQ and achievement is considered, allowing for equal probability of identification of an LD across IQ levels, thereby potentially enhancing identification rates. Research in the 1990s, however, failed to demonstrate valid differences on school-related measures between poorly achieving groups of students with an IQ/achievement discrepancy and those with poor school performance and no discrepancy.