Dyslexia Testing: What Is Dyslexia?

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Dyslexia, in the most basic terms, is a difficulty with words. Like all words that start with dys it refers to a problem, deficiency or lack. Lexia has to do with words and language. It shares an ancestry with other words like lecture. In particular, dyslexia refers to a difficulty with reading and writing words. This means that it’s possible for a dyslexic child to speak and understand language effortlessly, but have significant difficulty reading and writing the same language.

This broad definition also excludes general intelligence; a diagnosis of dyslexia is not an indication of low intelligence. In fact, dyslexia and other specific learning disabilities (as they are known in the literature) are, by definition, unexpected. In other words, true dyslexia is present only if all other aspects of intellectual development are normal. The condition and its effects are limited to the act of reading. In this article we are going to consider:

  • What happens when a dyslexic attempts to read
  • Current views on the origin and cause of dyslexia
  • The prevalence of dyslexia
  • The history of dyslexia in various disciplines
  • Other conditions that sometimes co-occur with dyslexia

Why is reading difficult?

It’s likely that you know someone who struggles with reading. This shouldn’t really surprise us, because reading is a complex act. It involves a wide range of processes and skills that all have to act at once, in the right way, in order to achieve the desired outcome of understanding a piece of text. For most of us, reading involves vision. Your eyes are currently moving across this text, back and forth, quite rapidly. In addition to this, reading involves an awareness of sound. When you began reading this article, you may have “heard” a voice (perhaps your own) reading the words to you, within your mind. To make matters even more complicated, reading relies on concepts in your mind. To take a small word like “read” as an example:

  • You took in the shape of the word with your eyes
  • You connected this shape to a sound or set of possible sounds
  • You ruled out an incorrect one like “red” and selected the right one for this context: “read”
  • You put this item into the sentence in order to understand what the writer was telling you about reading

All of this should have happened more or less instantaneously. For some people, however, it doesn’t. For a number of reasons, some people have difficulty at one or more of the stages we described above. When this happens, it becomes difficult to assemble the meaning of a text. In an age where reading is a vital life skill, this can cause significant problems.

It’s important to point out that not all people who experience difficulty in reading are dyslexic. Obviously, being able to read and write well depends on adequate training. If you don’t receive this training, you will probably find it difficult to read. Similarly, some kinds of brain injury or impairment may make complex tasks like reading difficult to achieve. However, when a child’s reading skills lag behind his or her overall ability, it is possible that dyslexia is present.

But where it is present, why? Some research suggests that dyslexia has a neurobiological basis. This means that its cause is in the brain. This goes some way in explaining why some children fail to achieve despite having adequate training and support. It also provides a way to make sense of the common occurrence of dyslexia within families. Recent research suggests that having a dyslexic family member significantly increases your chance of having it yourself. This is one of the reasons that family history is requested in many dyslexia tests.¹

How common is dyslexia?

It can be difficult to ascertain whether a child is dyslexic. As a result, determining exactly how many people are dyslexic is a tricky thing. This is because the definition of dyslexia, as we have seen, is not precise in the way that many other disorders are. What unifies all dyslexic people is that they find it difficult to read effectively for understanding. But this can mean many things. For some, it means they struggle particularly with certain letter symbols. For others, it might mean that they can identify individual words but can’t read fluently. Others can read moderately well but without understanding.

It’s difficult to arrive at a concrete figure, but dyslexia seems to affect a large number of people. Most estimates place the number at between 4 and 12 percent of a population.²  And this is worth knowing, because an early diagnosis is better than a late one. Later on we will delve into the ramifications of a dyslexia diagnosis, and what it means in the life of the child concerned.

Where does the term “dyslexia” come from?

The term dyslexia appeared for the first time in the late 19th century.³ Interestingly enough, an ophthalmologist came up with the term. He was working with adults who had lost their ability to read after a stroke. The term competed with “congenital word blindness” for some time. This clunkier terminology contains much of what we have already seen: “congenital” suggests an innate characteristic, and “blindness” suggests a deficit in something other than intelligence.

It was only some time later, in 1968, that the World Federation of Neurology met and defined dyslexia as a disorder in these terms:⁴

 “A disorder manifested by difficulty in learning to read despite conventional instruction, adequate intelligence, and socio-cultural opportunity. It is dependent upon fundamental cognitive disabilities which are frequently of constitutional origin.”

What other conditions can occur with dyslexia?

The study of learning disorders has developed since then. As various fields of study have converged on the problem of dyslexia, experts have begun to discover relationships between dyslexia and other conditions. In many cases, a person who has dyslexia will also experience at least one other condition or disorder.

Practitioners call these Specific Learning Disorders (SLDs) and estimate that the co-occurrence of conditions is actually typical. Generally, practitioners and clinicians talk about “co-occurrence”, which avoids the difficult question of whether one causes the other. The most important thing for parents to know is that a dyslexic child might experience more than one SLD. Some of the more well known of these are:

  • Attention Deficit Hyperactivity Disorder (ADHD): a condition that makes it difficult to focus on tasks or control impulses
  • Dyscalculia: difficulty with mathematical concepts and operations
  • Dysgraphia: difficulty with writing
  • Dyspraxia: a condition characterized by problems with coordination and movement

Because these commonly occur together, a full educational or neuropsychological assessment will typically use tools that measure skills relevant to all of these. Dyslexia tests are therefore seldom undertaken in isolation, but in the context of a broader evaluation of a child’s cognitive skills and behaviors.

Attention Deficit Hyperactivity Disorder (ADHD)

Children who show difficulty concentrating, resisting impulses or completing tasks may receive a diagnosis of Attention Deficit Disorder (ADD) or Attention Deficit Hyperactivity Disorder (ADHD). There is a wide range of opinion on the causes and treatment of ADHD, but it is clear that poor impulse control has a major effect on learning in general, and cognitively demanding tasks like reading in particular. Recent pediatric recommendations to manage this include a good diet and exercise after school.⁵


Dyscalculia is a term used to describe difficulties with number concepts and math. Children with this problem may have difficulty performing basic mathematical operations. At a more basic level, they might find it hard to recall objects in a sequence, or recognize patterns.


The term dysgraphia is used to describe a variety of difficulties with writing. In young children, these include problems with holding a pencil, forming letters and spelling words correctly. Dysgraphic writing often contains irregular letter spacing and sizing. Words and sentences may also appear skewed, rather than formed in a straight light. In older children, it can manifest in a tendency to write sentences that are either grammatically incorrect or incomplete.


Dyspraxia refers to difficulty with coordination and movement. It is also classified as Developmental Coordination Disorder (DCD). Children who receive a diagnosis of dyspraxia typically have difficulty manipulating objects with their hands, or moving in a deliberate and coordinated way. This shows up in tasks such as climbing stairs, or skipping. Children who lag behind developmental milestones such as crawling may be at risk of dyspraxia. Many of the symptoms that older children present are the same as those for other specific learning disabilities, such as difficulty concentrating or completing tasks.

If your child shows persistent difficulty in any of these areas, it may be necessary to undergo a comprehensive educational assessment. This will enable you to understand the causes of your child’s difficulties, and, if necessary, provide a diagnosis on which to base an action plan.

Learning disorders and the DSM

It is important to note that the status of dyslexia and all other conditions in this category is a matter of debate. One of the sources that professionals draw on is the Diagnostic and Statistical Manual (DSM), currently in its fifth edition. This is a tool compiled by the American Psychiatric Association (APA) that provides an index and description of mental disorders. The definitions and specifications in the DSM are a major influence on dyslexia testing and treatment. 

The most recent update to the DSM-5 posits that dyslexia and related terms are not defined with adequate precision. As a result, the Neurodevelopmental Work Group advises the use of the broader category of “Specific Learning Disability” (SLD) as a diagnosis, with each child’s particular deficit forming a description of that diagnosis. So, in these terms, dyslexia can be defined as a specific learning disorder with impairment in reading.⁷ The relevant code in the DSM-5 is 315.00. Similarly, other specific learning disabilities have their own codes. It is possible for a dyslexia test to reveal a number of these conditions co-occurring in one case.


Delve deeper

What are the signs of dyslexia?

The complexity of learning disabilities in general makes it difficult to pin-point a discrete set of definitive signs. This is further complicated by the fact that some behaviors or difficulties are interpreted differently depending on age and developmental stage. However, advances in dyslexia testing have enabled clinicians to link certain traits, behaviors and deficits to the presence of dyslexia. Here is a list of some of the more common ones: Read more…

How is dyslexia diagnosed?

Because a learning difficulty is a multi-faceted problem, it’s not always a straightforward matter to determine one is present. In this respect, dyslexia is very different to a disease or medical disorder. It’s important to remember that dyslexia is not a disease. It’s better to think of it as a mode or way of learning that is not optimally attuned to the requirements of education. Thankfully, it is possible to assess a child in order to determine whether he or she is dyslexic. This is crucial, because a diagnosis is the basis of any plan of treatment. Read more…

Which skills are measured in a dyslexia test?

An assessment does not measure one skill in isolation. Because of the nature of a specific learning disability, many different skills can be relevant to a diagnosis. There may be a deficit in visual, auditory or memory skills. A particular child’s deficit may exist in one, two or more skill areas. Read more…

How does a dyslexia test work?

If your child has gone through a screening and there are signs of a learning difficulty, the next step is usually a full educational assessment. These are known as educational assessments, psychoeducational assessments or evaluations. Before you book one, it’s important to know what is likely to happen before, during and after the assessment. Read more…

How much does it cost?

There is no single diagnostic dyslexia test. In order to obtain a dyslexia diagnosis, it is necessary to get a full educational or neuropsychological assessment. These assessments are complex, involving a large number of interrelated tests and tasks administered by a professional. Read more…

NEXT: Page 2: Signs of dyslexia

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