Severe Discrepancy

The term 'Severe Discrepancy' refers to one of the primary components of most State and/or local guidelines for determining if a student is eligible for special education services related to a specific learning disability. Although the real basis of a learning disability is an assumed information processing weakness, 'severe discrepancy' between ability and achievement is the standard method used to determine how much impact the processing problem has on a student's actual achievement. 'Discrepancy' is a measure of underachievement (the difference between ability and achievement) and 'severe' refers to how much underachievement is required by a given State or district before a student will qualify for special education services. Each State establishes its own criteria for determining a severe discrepancy.

In the 'old days' a standard 'rule of thumb' for establishing significant underachievement (and even for identifying a learning disability) was the determination of 'two years below grade level' in any of the basic academic skill areas (reading, math, or writing). Unfortunately, using that criteria, very few students below the 4th grade and over 25% of those above the 8th grade would qualify for service simply based upon that level of discrepancy. Over time much more sophisticated and statistically sound methods have been established to provide a more 'fair and accurate' measure of severe discrepancy across grades and ages of individual students.

Currently, the process of establishing a severe discrepancy typically involves the administration of individualized ability (IQ) and academic (achievement) tests and a direct comparison of obtained standard scores (generally based upon a student's age rather than grade placement). Standard scores typically are on a scale with a mean (or average score) of 100 and an average range extending roughly from 90 to 110. The obtained IQ and achievement scores are then compared in order to determine if a severe discrepancy exists.

Some States use a simple discrepancy criteria which establishes a standard score difference (for example, 20 points) between overall IQ score (usually the Full Scale IQ) and specific areas of achievement. Other States use a much more complex 'regression formula' to determine how significant a discrepancy is between ability and achievement. A regression formula is generally considered more accurate because it takes into consideration the correlation between ability and achievement tests and also the phenomenon of 'regression toward the mean' in which it is been found that students tend to achieve at a level a bit closer to the mean (100) than their IQ score would otherwise predict. In other words, a student with an IQ score of 85 is expected to have an achievement score somewhat higher than 85. The main thing to remember about a regression formula is that the number of points required for a 'severe discrepancy' is different depending upon how far the obtained IQ score is from the 'mean' of the test (100). For virtually all States or districts, the possible areas of severe discrepancy established by Federal guidelines include:

  • Basic Reading
  • Reading Comprehension
  • Math Calculation
  • Math Applications
  • Written Expression
  • Oral Expression
  • Listening Comprehension

Another thing to note about discrepancy calculations is that most States highly recommend (if not require) that a 'global' or 'Full Scale' IQ score be used when comparing a student's intellectual ability and achievement.




Return to the LDinfo Web Site to find out about any of the following topics (and more):

Learning disabilities - what is a learning disability (LD or SLD)?

Dyslexia: Dyslexia is a reading disability or reading disorder

Dysgraphia Dysgraphia is a writing disability or disorder

Dyscalculia Dyscalculia is a math disability or disorder

What is an attention deficit disorder (ADD, AD/HD, ADHD)?

Gifted LD: Can a student be gifted and LD?

Emotional/Behavioral issues and LD: Do LD students experience behavior problems or depression?

Section 504: What is a Section 504 plan?

What is special education?

What is processing?

What is a nonverbal learning disability (nonverbal LD or NLD)?

What is a central auditory processing disorder (CAPD)?

What is IDEA?

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