Intellectual Disability, Impairment or Delay?

Intellectual disability (ID), intellectual impairment or cognitive delay are terms used when a person has certain limitations in general mental functioning and in skills such as communicating, taking care of him or herself, and social skills. These limitations are generalized in that they effect many skill areas at once and they cause a child to learn and develop more slowly than a typical child. An older term that you may hear used occasionally is mental retardation.


Intellectual disability (ID),  is characterized by below-average intelligence or mental ability and a lack of skills necessary for day-to-day living. Children with ID can and do learn new skills, but they learn them more slowly and/or they have trouble retaining what they learned. There are varying degrees of intellectual disability, from mild to profound.

Someone with ID has limitations in two general areas:

Intellectual functioning. Also known as cognitive ability, intelligence or, often as it is measured, in terms on an “intelligence quotient” score (IQ score). This refers to a person’s general ability to learn, reason, make decisions, and solve problems.

Adaptive behaviors. Sometimes referred to as “daily living skills”. These are skills necessary for day-to-day life, such as being able to communicate effectively, interact with others, and take care of oneself.

ID occurs in roughly 1% of the child population. Of those affected, 85% have mild intellectual disability. This means they are just a little slower than average to learn new information or skills, and with the right support, most will be able to live independently as adults. It is important that ID in any form be diagnosed early, as the earlier treatment is started, the better the likelihood of a good outcome.

Signs of intellectual disability in children

There are many different signs of ID in children. Signs may appear during infancy, or they may not be noticeable until a child reaches school age. It often depends on the severity of the disability.

Some of the most common signs of ID are:

  • Rolling over, sitting up, crawling, or walking late
  • Talking late or having trouble with talking
  • Slow to master things like potty training, dressing, and feeding himself or herself
  • Difficulty remembering things
  • Inability to connect actions with consequences
  • An apparent lack of awareness of surroundings or low responsiveness to stimulation
  • Behavior problems such as explosive tantrums or uncommon social withdrawal
  • Difficulty with problem-solving or logical thinking

However, many children who exhibit such signs do not have ID! Children displaying a sign or two may have a more specific problem like a specific language disorder or other developmental delays that are not so generalized as is ID. In addition to seeking the help of a professional we encourage you to explore other pages on this site to get more information on how to possibly interpret the signs your child shows.

Again, ID can be mild or quite severe. Children with severe ID may are more likely to have other health problems as well ID. These problems may include seizures, mental or psychiatric disorders (anxiety, autism, etc.), lasting motor skill impairments, sensory deficits (e.g., vision or hearing problems), among others. What symptoms a child shows also depends a bit on the cause of their ID.

Causes of intellectual disability

ID results from a brain that does not develop and/or function normally. However, it is often difficult to identify the exact cause, or any one cause, of ID in any particular child. Still, there are some general common causes that have been noted:

  • Genetic conditions: These include disorders like Down Syndrome, Smith-Magenis Syndrome, and Fragile X.
  • Problems during pregnancy: Things that can interfere with fetal brain development include alcohol or other drug use, malnutrition, or certain infections.
  • Problems during childbirth: Intellectual disability may result if a baby is deprived of oxygen during childbirth (e.g., anoxia) or born extremely premature.
  • Illness or injury: Infections like meningitis, whooping cough, or the measles can lead to intellectual disability.
  • Severe head injury: Near-drowning, extreme malnutrition, exposure to toxic substances such as lead, and severe neglect or abuse can also cause it.
  • None of the above: In two-thirds of all children who have intellectual disability, the cause is unknown.

Can intellectual disability be prevented?

Certain causes of intellectual disability are preventable. The most common of these preventable disabilities is fetal alcohol syndrome, which happens when pregnant women drink alcohol, even though they shouldn’t. Getting proper prenatal care, taking prenatal vitamins, and getting vaccinated against certain infectious diseases can also lower the risk that your child will be born with intellectual disabilities.

In families with a history of genetic disorders or other signs, genetic testing may be recommended before conception. Certain types of ID, such as Down Syndrome,  are also related to genetic or chromosomal conditions that tend to occur more often as parents get older. Physicians will typically recommend genetic testing of the baby in-utero (before birth) to determine if the baby has one of these conditions. While this is not preventative in that the baby has already been conceived, such information can be very beneficial to  parents and doctors as they monitor the pregnancy and plan for birth and later interventions.  In some circumstances these children may also have physical deformations that can be surgically repaired before birth or shortly thereafter. See chorionic villi sampling procedure and amniocentesis.

Other tests throughout the pregnancy, such as ultrasound, are standard practice even if nothing is suspect. These tests may identify certain conditions associated with risks to the baby’s physical and cognitive health, and they can direct important next steps in prenatal care towards improvement.

Diagnosis of ID

Intellectual disability may be suspected for many different reasons (see signs above). A physical exam of the child may also reveal suggestive signs that are sometime linked to Intellectual Disabilities. In such cases, a doctor may order genetic or metabolic tests, blood tests, urine tests, imaging tests to look for structural problems in the brain or organs, or electroencephalograms (EEG) to look at brain function.

In children with developmental delays (see the “What is Normal – What’s Not” page of this website), the doctor will perform tests to rule out other problems such as hearing problems or certain neurological disorders. If no other cause can be found for the delays, the child may be referred for more in-depth testing.

For a child to be formally diagnosed as having ID, the law requires that two areas of function be documented: Intellectual functioning and adaptive behaviors. 

How  intellectual function is measured will vary depending on a number of child-factors, such as age, physical capabilities, and culture. It is important that the appropriate measure be used with your child and often second opinions are warranted.

Typically, the intellectual assessment will culminate in a rating or ranking of your child’s general intelligence  or cognitive ability relative to typically developing peers. A common cut-off that is used for ID is an intelligence quotient falling below the 3rd percentile. This means that the child’s intellectual performance on the test is as good as 3 out of the lowest scoring 100 children, or, put another way, the child performs worse than 97 out of 100 children. Other cut-offs may be used, and children with higher scores may still have an ID, but this cut-off is the most traditional. Depending on where the child lies—3rd,2nd, 1st percentiles—they may receive a more specific diagnosis such as mild, moderate, sever or profound ID.

To measure a child’s adaptive behaviors, a specialist will observe the child’s skills and compare them to other children of the same age. Formal screening devices are used in this assessment. Things that may be observed include how well the child can feed or dress himself or herself; how well the child is able to communicate with and understand others; and how the child interacts with family, friends, and other children of the same age.

The intellectual and adaptive assessments will involve interviews with the parents, observations of the child, and formal testing of intelligence and adaptive behaviors. A child is considered to have ID if he or she has deficits in both IQ and adaptive behaviors. If only one or the other is present, the child is not considered intellectually disabled under the law and formal practices.

Services available for people with ID

After a diagnosis of the ID is made, a team of professionals will more fully assess the child’s particular strengths and weaknesses towards designing interventions. This helps them determine how much and what kind of support the child will need in order to succeed at home, in school, and in the community. Not all, but some children will require medical care in addition to educational and home interventions.

For babies and toddlers, early intervention programs are available. A team of professionals works with parents to write an Individualized Family Service Plan, or IFSP. This document outlines the child’s specific needs and what services will help the child thrive. Early intervention may include speech therapy, occupational therapy, physical therapy, family counseling, training with special assistive devices, and/or nutrition services.

School-age children with intellectual disabilities (including preschoolers) are eligible for special education for free through the public school system. This is mandated by the Individuals With Disabilities Education Act (IDEA). Parents and educators work together to create an Individualized Education Program, or IEP, which outlines the child’s needs and the services the child will receive at school. The point of special education is to make adaptations, accommodations, and modifications that allow a child with an ID to succeed as much as possible in the classroom.

As a caregiver of a child with ID you should:

  • Learn everything you can about intellectual disabilities. The more you know, the better you can advocate  for your child
  • Encourage your child’s independence. Let your child try new things and encourage your child to do things by himself or herself. Provide guidance when it’s needed and give positive feedback when your child does something well or masters something new
  • Get your child involved in group activities. Taking an art class, participating in Scouts, and playing sports will help your child build social skills
  • Stay involved. By keeping in touch with your child’s teachers, you’ll be able to follow his or her progress and reinforce what your child is learning at school through practice at home
  • Keep careful records at home of all testing, doctor visits, IEP meetings, etc. This will help you track progress and have easy access to answer questions as the child grows
  • Get to know other parents of intellectually disabled children. They can be a great source of advice and emotional support. See support groups at: 
  • See other links on this web page including those under Resources

General Discussion

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