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Assessing Learning Disabilities

By Peter Chaban

Learning disabilities involve difficulties with information processing, especially language-based information. Before testing for possible learning disabilities, it is important to rule out other factors that could be interfering with learning. These might include visual, hearing, or motor impairments, environmental or cultural factors, or acquired brain injury.

If a learning disability excludes so many factors, then the question becomes ‘how is it identified?’ One approach is to demonstrate a gap between a student’s academic performance and her potential to achieve. This approach to assessment is often referred to as the ‘discrepancy formula’. The identification of this discrepancy is done through the use of standardized tests, which are administered and interpreted by a qualified professional, usually a registered psychologist or psycho-educational consultant. A standardized test must meet rigorous criteria for validity and reliability. Standardized tests are initially administered to a large number of children of all ages and backgrounds. The resulting scores are then used to establish a range of age and grade-based standard scores, or norms. The individual test-taker’s score can then be compared to these scores in order to determine whether she is at, above, or below average for her age or grade. As well, test administrators must follow strict procedures for administering and interpreting the tests. These tests yield scores that estimate the general intelligence (intelligence quotient or IQ) of the student, her academic achievement relative to established norms, and additional information about skills such as memory and the ability to focus attention.

The psychologist can then identify the size of the discrepancy between potential to achieve as measured by an IQ score, and actual achievement as measured by performance on a standardized test of reading or math. Although measuring this discrepancy is central to the discrepancy approach in assessing learning disabilities, it is important to note that many other factors, including the student’s cognitive profile, academic, and personal history should be considered in diagnosing learning disabilities and making recommendations for remediation.

The use of standardized tests and a discrepancy formula for diagnosing learning disabilities is not without controversy. One objection is that norms of different standardized tests have been developed by administering the tests to different groups of children and youth. Beacuase of this, opponents of the use of standardized tests argue test scores based on norms derived from different groups cannot be accurately compared.

Another criticism is that these tests do not accurately reflect the competencies and skills of students who have recently immigrated to Canada because of linguistic and cultural biases. It is the responsibility of the psychologist to decide whether certain tests are appropriate for new Canadian students. It has also been suggested that relying on the discrepancy formula delays access to special education service for younger students. Often school boards demand that a two or three grade discrepancy be present As a result, students are not identified until Grade 3 or 4 for special education support.

Supporters of the discrepancy formula argue that school administrators should use non-standardized screening tools in the early grades, as well as teacher observations to flag students who are struggling. These students should then receive extra help until they are tested in Grades 3 and 4.

Finally, some researchers have argued that measuring IQ is irrelevant to assessing learning disabilities. They argue that the core deficits associated with learning disabilities, for example the difficulty processing certain types of speech sounds associated with reading disability, are independent of IQ. A child with this deficit and an IQ score in the lower range of normal would be denied special education service under a discrepancy formula. These researchers propose eliminating the discrepancy formula altogether and assessing learning disabilities as they relate to specific tasks. For example, a student might have a learning disability specific to reading or mathematics. The assessment would then focus specifically on the particular difficulty that the student is having. For example, a reading based learning disability would be assessed based on the components of reading. The same strategy would be applied to math or writing difficulties. In general, one would want the assessment to reflect curriculum-based expectations.

Another approach to treatment and remediation of learning disability that is becoming widely adopted in United States is called Response to Intervention (RTI), or multi-tiered instruction.  In this model, students are screened when they begin reading instruction to identify at-risk students.  All students are then followed with frequent testing to make certain that they are learning at an appropriate rate.  Those that are falling behind are immediately assigned to a first tier of evidence-based intervention.  If they respond, they are returned to regular instruction.  Those who do not respond are provided with a more intensive, second-tier intervention, often in a special, low-ratio classroom.  Again, those that respond are returned to the standard instructional programme; those who do not respond may be placed in a third-tier intervention if it is available in the student's school board. Often it is at this level that a psychoeducational assessment may be provided and diagnosis of learning disability made, if appropriate. 

Whatever approach is used to diagnose a learning disability, it is important that the assessment be performed by a qualified professional, that the tests selected are valid and reliable, and that the information gathered, its interpretation, and the resulting recommendations are relevant to the student’s needs and unique situation.

Peter Chaban is a teacher researcher, head of the School Liaison Team, Community Health Systems Resource Group at the Hospital for Sick Children, and learning disabilities representative for the Ontario Minister's Advisory Council on Special Education.

Learning & Education columns by Peter Chaban


Peter Chaban is a teacher researcher, head of the School Liaison Team, Community Health Systems Resource Group at the Hospital for Sick Children, and learning disabilities representative for the Ontario Minister's Advisory Council on Special Education.

Learning & Education columns by Peter Chaban