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Page 2: The IQ-Achievement Discrepancy Model
Click on the movie below to watch the Rosa Parks Elementary School S-Team members discuss their current method of identifying struggling readers (time: 0:53).
What Is the IQ-Achievement Discrepancy Model?
The IQ-achievement discrepancy model is the traditional method used to determine whether a student has a learning disability and needs special education services. The discrepancy model is based on the concept of the normal curve (click here for a review of the normal curve). The discrepancy model assesses whether a substantial difference, or discrepancy, exists between a student’s scores on an individualized test of general intelligence (that is, an IQ test such as WISC-IV) and his or her scores obtained for one or more areas of academic achievement (e.g., the Woodcock-Johnson Achievement Test). The accepted criteria for identifying a student as having a learning disability with the IQ-achievement discrepancy is a difference of at least two standard deviations (30 points).
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A student with an average IQ score (around 100) is expected to receive average (or grade-level) scores on achievement tests. So a fourth grader with an average IQ score (represented by the red bar in the figure to the left) and a reading achievement score at the fourth-grade level (represented by the yellow bar) is performing as expected.
Standard Score is the score obtained on a standardized test, where the mean is set at 100 and the standard deviation is usually set at 15.
Standard Deviation is how much a student’s score deviates from the mean, or average, score.
Grade Equivalents are expressed in the form “grade.months,” so here the “average reader” (4.7) is reading at the level of a student in the seventh month of the fourth grade.
IQ Score is an overall score obtained on a standardized test of intelligence. For the scores shown on this graph, the average scores fall between 85 and 115, and 100 is the mean.
Reading Score is an overall score obtained on a standardized test of reading achievement. For the scores shown on this graph, the average scores fall between 85 and 115, and 100 is the mean.
Discrepancy is the amount of difference between a student’s scores on a standardized test of intelligence and a standardized test of achievement.
The figure to the right shows scores for a different fourth grader. This student’s IQ score is 85 (again, represented by the red bar), and his reading score is also 85 (represented by the yellow bar), showing that his reading ability is only equivalent to a second-grade level. These scores indicate that this student’s reading ability is commensurate with his intelligence test scores. In other words, one would expect his reading achievement to match his ability level. Unfortunately, though it is obvious that such a student is a “low achiever” and would require extra help, he would not qualify (according to federal law) for special education services as a student with a learning disability.
Students with learning disabilities, however, exhibit unexpected learning difficulties because their level of achievement is far below what is predicted by their IQ scores. This figure shows scores for a fourth-grade student who qualifies for special education services because of a reading disability. The student demonstrates a discrepancy between expected achievement and actual achievement. He has an IQ score of 100 (as indicated by the red bar), but his reading score is 68 (as indicated by the yellow bar). Though his IQ score indicates that he should be reading at least at the fourth-grade level, he is instead reading at the first-grade level. Because of the discrepancy, this student has been identified as having a reading disability.
Concerns About the IQ-Achievement Discrepancy Model
Many teachers, like those at Rosa Parks Elementary School, express concern and frustration that the IQ-achievement discrepancy model rarely identifies students with learning disabilities in the early grades. Rather, these students often struggle for years before they are finally identified.
Click on the movie below to learn why it can take so long for students to be identified as having learning disabilities and to then qualify for special education services (time: 1:46).
Another limitation of the IQ-achievement discrepancy model is that it does not assess or inform the quality of instruction received by students. Some students may be identified as having learning disabilities when, in reality, they simply have not experienced classroom instruction that meets their learning needs. Furthermore, the assessments that are used to identify a learning disability do not yield information that can easily be used to guide subsequent instruction.
Click on the audios below to hear two experts discuss other concerns about the IQ-achievement discrepancy model. Doug Fuchs is a national expert in the areas of reading instruction and learning disabilities. Leonard Baca is a nationally recognized leader in the areas of bilingual and multicultural special education.
Listen as Doug Fuchs discusses the issue of linguistic diversity in relation to administering and scoring progress monitoring probes (time: 1:45).
Doug Fuchs, PhD
Nicholas Hobbs Endowed Chair in Special Education
and Human Development
Peabody College, Vanderbilt University
Now listen to Leonard Baca discuss concerns about using Spanish translations of English language assessments (time: 1:05).
Leonard Baca, PhD
Director, BUENO Center
for Multicultural Education
University of Colorado, Boulder
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To summarize, here are some concerns about the IQ-achievement discrepancy model:
- Assessments do not always discriminate between disabilities and the results of inadequate teaching.
- Students can be misidentified due to teacher or testing bias.
- Typically, students must first fail in order to qualify for special education services.
- Results from assessments do not inform the instructional process.
- Many students do not meet the discrepancy criteria but would nevertheless benefit from early identification and support to remediate their skills.
Advantages of the IQ-Achievement Discrepancy Model
Although many professionals are frustrated with the IQ-achievement discrepancy model, the model does possess a few advantages that might appeal to some schools:
- The IQ-achievement discrepancy model is an established practice.
- It is relatively easy to employ.
- A teacher does not have to spend a great amount of time in the identification process because a certified diagnostician or school psychologist conducts the IQ and achievement tests.
- The identification procedure only requires a one-time assessment.