How specific are developmental disorders?

Developmental disorders like dyslexia and autism spectrum disorder have historically been viewed as specific and having a single explanation. But there are no simple explanations for these disorders, and children can have difficulties that are not captured by their diagnosis. Embracing the complexity of developmental disorders will lead to a better understanding of individual children and their needs.

Developmental disorders are typically described in terms of a “core deficit” in a specific area of learning. For example, Alex might have a diagnosis of dyslexia because of a difficulty with reading, while Leslie’s difficulty with arithmetic leads to a diagnosis of dyscalculia. These categorical diagnoses inform the types of intervention that Alex and Leslie receive to help them learn. But it is increasingly recognised that there are limitations to categorising children in this way.

“Children can have difficulties that are not captured by their diagnosis.”

In a paper published in 2020, Duncan Astle and Sue Fletcher-Watson argue that it’s time to move away from this core deficit approach. It is appealing and intuitive to see disorders as discrete, separate conditions, they say. But it’s not as simple as it seems. There is no universal cause that explains all diagnoses of dyslexia, for example.

Astle and Fletcher-Watson give the example of autism spectrum disorder, which researchers traditionally consider a deficit in “theory of mind”. Theory of mind is the understanding that the mental state of others differs from our own. Although impaired theory of mind is the dominant understanding of autism, it does not explain many factors that are common among autistic people, such as intense interests and sleep disturbances.

“There are limitations to categorising children in this way.”

When I ask Astle why the core deficit approach gained such prominence, he tells me there are a number of good reasons why researchers find it so appealing. “The most important reason is simplicity. All of us find a simpler story easier to digest. The researchers’ work becomes more widely understood and cited. It’s memorable and easy for people to identify with a particular researcher, and the rest of the field then spends a great deal of time either supporting or refuting the theory.”

Appreciating children’s individual differences

Contrary to the core deficit model, children with one developmental disorder often have other difficulties as well. Astle and Fletcher-Watson explain that it is rare for children with a reading impairment to have no difficulty in maths, for example, or vice versa. Alex is likely to find maths difficult, too, while Leslie may struggle with reading, yet this is not reflected in their diagnoses. In a paper published in 2019, Lien Peters and Daniel Ansari show that researchers often fail to recognise how one disorder may overlap with another. Those who study children with dyslexia, they say, tend not to measure arithmetic performance. The result, Astle says, is that “difficulties look more specific because of the design of the study”.

Both papers also point out that researchers tend not to study the differences between children who have the same disorder, focusing instead on similarities. They describe commonalities in children with dyscalculia, for example, rather than looking at individual differences. This makes it appear that children with dyscalculia are very similar, although they may have quite different strengths and weaknesses.

“Embracing this complexity will lead to a better understanding of the issues that have an impact on people’s lives.”

According to Astle and Fletcher-Watson, “the research in neurodevelopmental diversity is at a potential tipping point”. They argue that embracing this complexity will lead to a better understanding of the issues that have an impact on people’s lives – and of how to deliver successful interventions for those who need help. Moving away from the core deficit approach, Astle observes, will “provide a powerful new step forward in theory”.

It’s time to stop thinking about children in terms of specific deficits, and start thinking about them as individuals with strengths as well as impairments, so that all children can get the help they need. As Astle points out, “understanding someone’s strengths as well as their difficulties might be crucial for designing effective interventions”.