For many years, teachers have followed a fairly course of action for getting help for students struggling in their classrooms. In many schools, this course of action involves referring a student to a school-based team (often called an Instructional Support Team). This team can recommend strategies based on a student's individual needs to help the student succeed within the general classroom. When a disability is suspected, the student can be referred for an evaluation by a school psychologist. If, in this evaluation, the referred student demonstrates an educational need and is found to be eligible under one or more of the 13 disability categories (as defined by federal law), he may qualify to receive interventions in the form of special education. Just one of these 13 categories, Specific Learning Disability (or simply LD), accounts for about half of all students who become eligible for special ed.
The Discrepancy Model
In an evaluation under the traditional discrepancy model, the referred student is administered a series, or battery, of standardized tests. A typical testing battery is comprised of two key pieces: 1) the IQ test, intended to establish the student's mental ability, or learning potential; and 2) the Achievement Test, meant to show where the student is performing academically in relation to his ability.
This two-pronged approach might seem logical enough: Estimate the student's potential using an IQ test. Then compare that level of potential with how the student is achieving. See just how far below potential the student is actually performing. So how does this evaluation method present a problem?
Unfortunately, as traditionally practiced, what otherwise might seem like a sound approach actually presents a number of unintended consequences. And the discrepancy model has earned a nickname that seems at odds with the concept of early intervention--the 'wait to fail' model.
Dr. White's Ability-Achievement Discrepancy Analysis