Intellectual Disability: What it is, what it isn't and other common questions
What is an Intellectual Disability?
Intellectual Disability (ID; also referred to as Learning Disability or Learning Difficulties) is a term used when a person has certain limitations in cognitive functioning and adaptive skills, including communication, social and self-care skills. These limitations can cause an individual to develop and learn more slowly or differently than a typically developing child.
Intellectual Disability is the most common developmental disability and it is a lifelong condition. Individuals with Intellectual Disability are likely to need some degree of support for the rest of their lives in order to live independently.
In order to receive a diagnosis of an Intellectual Disability, these three criteria must be met:
Significant impairment in cognitive functioning
Significant limitations in adaptive functioning (skills needed to live, work, and play in the community, such as communication or self-care)
The condition manifests itself before the age of 18
Some people refer to Intellectual Disability as ‘Learning Difficulties’, when in actual fact a Specific Learning Difficulty is when someone has a specific area of their functioning where they struggle and the rest of their functioning is within normal limits. Examples of Specific Learning Difficulties include Dyslexia and Dyscalculia.
In Education settings, people may refer to ‘moderate learning difficulty’ or ‘severe learning difficulty’ when they actually mean Intellectual Disability. However, terminology is different in Education and other settings so it is important to clarify exactly what someone means.
What Causes Intellectual Disability?
Intellectual Disability can be caused by injury, disease, or a problem in the brain. For the majority of children, the cause of their Intellectual Disability is unknown. Some causes of intellectual disability – such as Down syndrome, Foetal Alcohol Syndrome, Fragile X syndrome, birth defects, and infections – can happen before birth. Some happen while a baby is being born or soon after birth. Other causes of Intellectual Disability do not occur until a child is older; these might include severe head injury, infections or stroke.
What Are the Most Common Causes?
The most common causes of Intellectual Disability are:
Sometimes an Intellectual Disability is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons. Examples of genetic conditions are Down syndrome, Fragile X syndrome, and phenylketonuria (PKU).
Complications during pregnancy
An Intellectual Disability can result when the baby does not develop inside the mother properly. For example, there may be a problem with the way the baby’s cells divide. A woman who drinks alcohol or gets an infection like Rubella during pregnancy may also have a baby with an Intellectual Disability.
Problems during birth
If there are complications during labour and birth, such as a baby not getting enough oxygen, this may result in the child having an Intellectual Disability.
Diseases or toxic exposure
Diseases like whooping cough, the measles, or meningitis can cause Intellectual Disabilities. They can also be caused by extreme malnutrition, not getting appropriate medical care, or by being exposed to poisons like lead or mercury.
We know that Intellectual Disability is not contagious: you can’t catch an Intellectual Disability from anyone else. We also know it’s not a type of mental illness, like depression. There are no cures for Intellectual Disability. However, children with Intellectual Disabilities can learn to do many things, they may just take more time or learn differently than other people and are likely to require extra support on an ongoing basis.
Other factors associated with an increased risk of a child having Intellectual Disability include:
Advanced maternal age
Maternal alcohol or tobacco use during pregnancy
Maternal diabetes, hypertension, epilepsy and asthma
Male sex (many more boys are born with Intellectual Disability than girls)
A strong family history of Intellectual Disability
How Common Are Intellectual Disabilities?
Approximately 1-3 percent of the global population has an Intellectual Disability -- as many as 200 million people.
Intellectual Disability is significantly more common in low-income countries – 16.41 in every 1,000 people. Disabilities overall are more common in low-income countries.
Is Intellectual Disability the same as Global Developmental Delay?
The term ‘developmental delay’ means that a child is not meeting a developmental milestone within the expected age limits. This may be in one area (e.g. speech/language, motor skills, toileting etc) or multiple areas. If the delay is in multiple areas, the child may be described as having Global Developmental Delay. Some children may be delayed in all areas of their functioning.
Global Developmental Delay is a diagnosis that should only be used for children aged 5 or under and should be used as a temporary diagnosis until a full assessment of a child’s skills can be undertaken.
Some children who have delays in their development make progress and ‘catch up’ with their same age peers. However, we know from research and clinical practice that if a child is already showing delays in multiple areas and has not ‘caught up’ by around the age of 5, they are unlikely to ‘catch up’ to the same level as their same age peers. They will continue to learn, develop and make progress, but there is likely to always be a gap between their skills and abilities and those of their same age peers and this is likely to widen as they get older.
Therefore, a child who has been described as having Global Developmental Delay who is 5 or older should be assessed to see if they meet criteria for a formal diagnosis of Intellectual Disability. It is unhelpful and inaccurate to continue using the term Global Developmental Delay beyond 5 years old because the word ‘delay’ infers that the person will catch up. This can confuse parents and set up unrealistic expectations that their child will ‘catch up’, when in reality this is highly unlikely.
How Do I Know If a Child Has Intellectual Disability?
In order to ascertain whether the diagnostic criteria of having impaired cognitive functioning and impaired adaptive functioning are met, a comprehensive assessment should be undertaken.
Children identified as having Global Developmental Delay who are school aged may already have an Education Health and Care (EHC) Plan (previously called a statement of special educational needs) and are more likely to be attending a specialist educational setting.
If they are attending a mainstream educational provision, it is more likely that they will require additional support from adults. It may be that a child is very behind, struggling to cope and/or demonstrating difficult behaviours if they are not coping in their educational setting.
In order to formally identify whether someone meets criteria for a diagnosis of Intellectual Disability, their cognitive functioning and adaptive functioning needs to be assessed.
Only Clinical or Educational Psychologists can assess cognitive functioning. This is usually done through completion of tests such as the Wechsler Children’s Intelligence Scale (WISC) or the Wechsler Preschool and Primary Intelligence Scale (WPPSI). Many Educational Psychologists assess cognitive functioning using the British Ability Scales (BAS).
A cognitive assessment measures an individual’s thinking and learning skills in different areas, including their visuospatial ability, verbal comprehension, working memory, speed of processing information and problem solving. A profile of an individual’s cognitive strengths and weaknesses is put together and this is compared with what would be expected for their age.
An overall score is also usually calculated to summarise an individual’s overall cognitive ability called an IQ (Intellectual Quotient) score or GAI (General Ability Index). However, it may not be possible to compute a valid overall score if there are large discrepancies between an individual’s scores in different areas.
If the overall score is below 70, this indicates significant cognitive impairment. Average scores range from 90-110. It is important to note that a cognitive assessment is a snapshot of a person’s skills and abilities on that particular day.
If a full cognitive assessment is not possible to complete with an individual, other measures may be used to estimate the individual’s functioning, such as the Raven’s Matrices. It is important to check whether an Educational Psychologist has completed a cognitive assessment too.
Other indicators of an individual’s level of cognitive functioning include how they are getting on academically at school.
A very rough rule of thumb is that if an individual appears to be functioning at around half their chronological age or below in terms of their thinking, learning and understanding (e.g. an 8 year old functioning like a 4 year old), then they are likely to have an Intellectual Disability and this should be formally assessed to rule this in or out.
An assessment of adaptive functioning should also be completed, using a questionnaire that measures this and compares it to other individuals of the same age. These include the Adaptive Behaviour Assessment System (ABAS) and the Vineland Adaptive Behaviour Scales. Clinical Psychologists should be able to complete these assessments.
Adaptive behaviour refers to the practical and independence skills that people need in everyday life, such as keeping safe, self-care, social skills and being able to access the community.
In addition to impaired cognitive and adaptive functioning, individuals with an Intellectual Disability also often display the following behaviours and traits:
Sensory processing and integration difficulties
Rigidity and dislike of change
Difficulties with communication
Social immaturity and not fitting in with peers
Other behaviours and interests that are like much younger children
Depending on their level of impairment, an individual may be described as having a Mild, Moderate, Severe or Profound Intellectual Disability. Individuals with Profound Intellectual Disability often have multiple physical and sensory disabilities and life limiting conditions.
For many children who meet criteria for an Intellectual Disability, they will have already had input from a range of other professionals and/or agencies, or may need this.
These are likely to include the following (in no particular order):
Speech and Language Therapists – if a child’s speech, language and/or communication development is delayed or disordered; or if a child has difficulties with oral motor movements (e.g. with swallowing).
Educational Psychologists – if a child is struggling to access learning or make progress in their educational setting, an Educational Psychologist may either directly assess them or provide staff in the educational setting with advice and strategies to support the child.
Occupational Therapists – if a child’s fine and/or gross motor development is delayed or disordered; or if the child has struggled to develop everyday living skills (e.g. toileting, eating, dressing, self-care); some Occupational Therapists also assess sensory processing and integration difficulties, but not all.
Physiotherapists – if problems have been identified with the child’s physical function, movement, gait or posture they may have support from a physiotherapist.
Paediatricians – if a child has any physical health conditions (e.g. epilepsy, gastroesophageal reflux, constipation) or there are other general concerns about their functioning, they are likely to have been seen by a Community Paediatrician or a Paediatric Consultant from a particular medical specialty in a hospital setting.
Geneticists – if there is a family history of genetic disorders or a child is noted to have features of a known genetic condition, they may be referred to a Geneticist.
Specialist Nurses – a Community Learning Disability Nurse, School Nurse or Children’s Nurse may be involved to support a child and their family with issues such as toileting issues.
Social Workers – if a family receives respite or the individual is around 16 and transitioning to post-16 education, they may have a social worker who assesses their support needs (as opposed to being involved for safeguarding reasons).
Useful resources for further reading
Psych4Schools have created a really useful booklet for staff in mainstream educational settings called Working with Children with an Intellectual Disability
Contact (previously known as Contact a Family) also have a really useful website. The videos they have produced with parents sharing their experiences of what it is like to have a child with Intellectual Disability are really well done, see their YouTube channel.
You can also find out what is available locally in your area for children with additional needs by checking out The Local Offer website.
You can find your local Special Educational Needs and Disabilities (SEND) Information Support Service via this website and they can offer advice on how to access support for your child.
Dr Fleur-Michelle Hope | Senior Clinical Psychologist | BSc (Hons) MPhil DClinPsychol CPsychol AFBPsS