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How does one differentiate between mild, moderate, and severe LDs? How can I tailor my interventions/strategies to the needs of students with differing degrees of learning disabilities?

Answered by Dr. Maria Kokai M.A., PhD., C.Psyc., Chief Psychologist with the Toronto Catholic District School Board.

This article has been updated to reflect the new set of guidelines for diagnosis created by the Cross-Sectoral Psychology Working Group on Learning Disabilities, adopted by the Ontario Psychological Association in 2018, and the Learning Disabilities Association of Ontario in 2019.

Learning disabilities (LDs) are considered to be due to genetic, congenital and/or acquired neurobiological factors that result in academic impairments, combined with at least average abilities essential for thinking and reasoning, and deficits in one or more psychological processes related to learning. In view of the biological/neuropsychological nature of the disability, the formulation and communication of a diagnosis of learning disabilities is a complex process that requires professional training and skill. Professionals from a variety of disciplines (e.g., psychology, education, speech-language pathology, occupational therapy, medicine, audiology, etc.) play a significant role in identifying “at-risk” individuals and in contributing to the evaluation, as well as to the development and implementation of a range of interventions. In Ontario, however, the communication of a diagnosis is controlled under the Regulated Health Professions Act, and may only be performed by appropriately qualified members of the College of Psychologists  and the College of Physicians and Surgeons.

Diagnostic Criteria for Learning Disabilities

According to the Guidelines of Diagnosis and Assessment of Children, Adolescents and Adults with Learning Disabilities (Ontario Psychological Association, 2020), all of the following criteria must be met for a diagnosis of a learning disability to be made:

  1. “History of academic functioning below the level typically expected for individuals of the same chronological age, or the need for excessive time or support to develop or maintain typical levels of academic functioning.”
  2. “Below average academic achievement (i.e., at least one standard deviation below the mean) in at least one of”: reading, writing, or mathematics.
  3. “Evidence that the difficulties in reading, writing, or mathematics are logically related to deficits in psychological processes.”
  4. “At least average abilities essential for thinking and reasoning.”
  5. “Evidence that the difficulties in reading, writing, or mathematics cannot be accounted for primarily by factors such as:
    • Other conditions or disorders (e.g., intellectual disabilities, uncorrected visual or auditory acuity, physical or chronic health disabilities, other neurodevelopmental disorders, or internalizing or externalizing disorders);
    • Environmental factors (e.g., psychosocial adversity, inadequate or inappropriate educational
    • Insufficient motivation or effort;
    • Cultural or linguistic diversity. "

(taken from the Guidelines of Diagnosis and Assessment of Children, Adolescents and Adults with Learning Disabilities, Ontario Psychological Association, 2020)

Although there are no formalized criteria to define what constitutes a mild, moderate, or severe LD, generally we can determine the severity of the LD by the following:

  • The number of skill areas affected by the LD (such as different areas of academic skills, life skills, social skills, etc.); and
  • The severity of the deficits in psychological processes and the degree of impairment in the skill areas affected by the LD and the degree to which the impairment interferes with the person’s everyday functioning, despite appropriate intervention/remediation (in the different academic skills, life skills, social skills, etc.).

Typically, the more skill areas are affected, and the higher the degree of impairment, the more severe the LD is.

For example, a student with some deficits in phonological processing may have difficulties in learning to decode words, but once basic reading skills have been acquired, is able to read. However, he/she will continue to require a longer time to read and understand paragraphs. This would be consistent with a mild LD.

On the other hand, if a student has deficits in a number of psychological processes, for example working memory, processing speed, phonological processing and language processing, many academic skills connected with these can be significantly impaired: oral communication and listening comprehension, reading decoding as well as reading comprehension, spelling, and writing, understanding the language of math, remembering instructions, completing mental computations, etc. The significant impairments in these areas will inevitably impact most of the other academic areas (including math), as well as daily communication and social functioning, making the LD severe.

The programming and support required needs to be tailored to the individual needs of the person with LDs, as the impact of LDs vary widely.

Taking the above example for a mild LD, with specific and focused reading remediation, the reading skills can be improved, while all the other academic, and social skills are age-appropriate. The student will be able to function at grade level with some accommodations (e.g. longer time provided for reading, relying on other ways to access information, etc.), and no other academic or other skill areas will be affected.

In the case of the second example, both intensive remediation/intervention to improve these skills (reading, decoding, vocabulary building, social communication skill instruction, etc.), as well as Assistive Technology and appropriate accommodations to access the curriculum in all subject areas will be required.


Ontario Psychological Association (2020). Guidelines for Diagnosis and Assessment of Children, Adolescents and Adults with Learning Disabilities. Consensus statement and Supporting Documents. https://www.psych.on.ca/OPA/media/Members/Guidelines/OPA-Guidelines-for-Diagnosis-and-Assessment-of-Learning-Disabilities-03-2020.pdf?ext=.pdf

Related Resources on the LD@school Website 

Click here to access the Ask the Experts answer to the question, “How are LDs in mathematics typically diagnosed?” by Dr. Todd Cunningham. 

Click here to access the practice-informed summary, “Universal Design for Learning (UDL)”. 

Click here to access the practice-informed summary, “Differentiated Instruction”. 

Click here to access the slide presentation, “Demystifying the Psycho-Educational Assessment Report”. 

Click here to access the article and video, “York Waterfall Chart: Understanding Learning Disabilities – How Processing Affects Learning”. 

Click here to view the video, “The Tiered Approach”, filmed in partnership with the Thunder Bay Catholic District School Board (TBCDSB). 

Picture of Dr. Maria Kokai

Dr. Maria Kokai holds a Ph.D. in clinical psychology and is the former Chief Psychologist for The Toronto Catholic District School Board. Prior to her Chief Psychologist position, Dr. Kokai worked as a school psychologist for 20 years. As a school psychologist, and in her role as Chief Psychologist, she was regularly involved in professional development for educators, and in the selection, implementation, and evaluation of various board-wide evidence-based intervention programs in the areas of LD, resilience and mental health.  She served as President of the Association of Chief Psychologists with Ontario School Boards and has been a member of the Ontario Psychological Association, as well as the OPA Section on Psychology in Education and OPA-Ministry of Education Liaison Committee. Dr. Kokai also serves as an advisory member of the LDAO’s LD@school project.