IQ-Achievement Discrepancy Model of Learning Disabilities

Under this model, educational teams usually lead by a psychologist showed a discrepancy between overall intelligence and skill achievement. Typically, this discrepancy needed to be greater than 2.0 standard deviations, or 30 points. For example, a child with an overall intelligence score of 100 as measured by a standardized test such as the Wechsler Intelligence Scale for Children, but a skill performance score of  70 on another standardized test would qualify a child as being learning disabled.



The problem with this qualification model is that it required a child to be essentially failing in order to receive special education services in the schools. In addition, special education services typically would not start until third grade or later, as there was not a big enough discrepancy between overall IQ and    achievement until this point.

A positive of using this model, in my opinion, is that the psychologists or LD teachers often performed a number of processing tests such as can be found on the Woodcock Johnson Test of Cognitive Abilities in order to look at individual processing strengths and weaknesses.

Johnson and Myklebust's Learning Disabilities: Educational Principles and Practice published in 1963  lead the field of learning disabilities.  Lovingly re-titled the "green bible"  by students of Dr. Johnson.

Johnson and Myklebust's Learning Disabilities: Educational Principles and Practice published in 1963  lead the field of learning disabilities.  Lovingly re-titled the "green bible"  by students of Dr. Johnson.

At the Northwestern University Learning Disabilities Clinic, we found these processing tests helpful for determining in what ways a child best acquired, stored, and retrieved information.  Under the guidance of a pioneer in the field of learning disabilities, Dr. Doris Johnson  with her "green bible," NU Wildcats for more than 30 years learned how to analyze input and output systems for kids, and how to adjust teaching accordingly.

We all have strengths in different areas. For example, if I’m learning something new, I have to talk myself through it.   I attend an aerial arts class where circus teachers shows us what to do on equipment such as the trapeze. Most students in the class are visual kinesthetic learners, in that they can just watch and do.  I’m the person in the corner talking through every move and asking thousands of questions before I get up on the trapeze, as my verbal abilities far exceed my spatial skills and visual processing abilities.  I know I learn best this way, and I use it to learn.  I’m also a person who cannot put together anything from IKEA that comes with pictures but no words, so I know that I need to find help before attempting tasks like these or risk losing my sanity.

This is me hanging upside down after talking myself down from my fear of heights and talking myself through how to get up and out of this.  

This is me hanging upside down after talking myself down from my fear of heights and talking myself through how to get up and out of this.


The problem is that children, especially kids who struggle with learning, often do not often know how they learn best. They don’t have strategies like I do in order to help themselves in school and in life.  Processing tests help teachers determine this quickly. When working with older children with learning disabilities, I like to tell them how they learn best in order to empower them. For example, “Joe, you have really strong abilities to see information and do something with it. However, when you just hear things, it’s harder for you to remember.  I bet it's hard for you when your teacher is standing up in front just talking, but you are really good at puzzles."  An accurate processing report makes a child's face light up, as someone finally "gets it."

Using processing abilities, we can help  children learn study skills playing on their strengths. We can also accommodate a child's weaknesses  by adapting learning inputs and methods of assessment.

A few real world examples:

1. A child presents with stagnant scores on curriculum based reading measures of oral reading fluency.  The child is assessed for special education services and it's determined that the child has moderate word retrieval difficulty by the speech-language pathologist. Word retrieval can affect the speed of oral reading fluency.  Therefore the team decides to provide a testing accommodation for the word retrieval processing difficulty, using silent reading with multiple choice answers in lieu of oral reading fluency to assess progress.

2. Another child has difficulties with visual processing.  In order to accommodate these needs, teachers limit the number of math questions on a page for the child. Within writing, teachers can accommodate by  providing simple graphic organizers without extra words and cute decorations as these can be distracting for this child.   The child will also be instructed to use a notecard while reading in order to eliminate excessive visual input, and a teacher will spend extra time helping a child learn how to read content books like social studies and science where text is placed all over the page in different blocks and bubbles.

 3. A child receives a diagnosis of Central Auditory Processing Disorder from an audiologist.  With this type of processing difficulty, a child may have difficulty discriminating the teacher's voice within classroom background noise.  Accommodations may include pairing the student with a direction buddy who can repeat directions as needed and placement of the child next to the teacher during lecture-style instruction.  The teacher will also be instructed not to play music during partner-work times, as this will may make it harder for the student to work quietly with a friend.

Can we try out all these accommodations without processing tests? Yes. However, this can at times result in a menu listing of similar classroom adaptions for every child, which is not as effective.


Response to Intervention   

Under an RTI model, children are placed into tiers of instruction. Tier 1 is the entire class, general education instruction.  Under best practice RTI, all children are universally benchmarked several times a year in various academic skill areas.   The data from the benchmarks helps determine which children are falling below average compared to their peers.  Using this data, children can be grouped into a second Tier, or Tier 2 services.  Usually, Tier 2 entails a smaller sized group for instruction, often in addition to Tier 1 academic content.  Depending on the school, Tier 2 may be review of materials learned in Tier 1 or it may be a supplemental program. Children at Tier 2 are continually monitored to ensure that they progress. If  they do not, then children move to Tier 3.

Sometimes, a school will provide Tier 3 support without a special education qualification if the team feels that the child's skills will improve in a timely manner allowing for movement out of Tier 3 small group instruction within the year.  However, many schools do consider meeting as a special education team with the parents in order to qualify a child as learning disabled at this point as well.   Tier 3 is typically provided by special education teachers or speech-language pathologists.  Tier 3 is different from Tier 2 in that the instruction is individualized, whereas in Tier 1 and  2 there are group learning goals. The thought is that the child has not made progress within a big group, nor a medium group. In Tier 3, specialists need to do something individualized to help this child progress.  As part of an individualized education plan, a team including parents will determine a child's strengths and weaknesses and create individual learning goals, called an IEP (Individual Education Plan).












One of the problems with the RTI  model, at least in my opinion, is that many special education teams no longer specifically assess processing abilities as it is not required for learning disabilities qualification under the Individuals with Disabilities Act of 2004.   An inventory of strengths and weaknesses is still required as part of the learning disabilities identification process.  However,  the thought is that the team can test out different teaching methods and see if the child responds to the instruction, as the RTI name states.  In my opinion,  this method can times miss weaknesses and it can waste time in trial and error whereas a general cognitive profile hypothesis confirmed by targeted processing tests can help pinpoint strengths and weaknesses directly in order to adapt the teaching methods and accommodate specific needs to individual children in a Tier 3,  special education setting.

The pros of the RTI model are that teachers do not wait until a child is failing before doing something different than general education, like they often did under the discrepancy model.  RTI is a much more proactive, preventative model. Many schools begin RTI services as early as pre-school and kindergarten. Another pro of the RTI model is that it puts less emphasis on IQ testing.  Intelligence is a malleable trait, and if our goal is to teach children, assigning a cap to their capabilities is unnecessary.