Intellectual Disabilities: Definition, Levels, Causes, Prevention & Treatment

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Clinical Features of Personality Disorders: Identity & Interpersonal Difficulties

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:06 Intellectual Disability
  • 0:43 Levels of Intellectual…
  • 2:53 Causes and Treatment
  • 5:18 Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed Audio mode

Recommended Lessons and Courses for You

Lesson Transcript
Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

Expert Contributor
Jennifer Levitas

Jennifer has a Ph.D. in Psychology. She's taught multiple college-level psychology courses and been published in several academic journals.

People with intellectual disabilities have low IQs and problems with daily functioning. In this lesson, we'll examine the levels of intellectual disabilities as well as the causes and treatments of them.

Intellectual Disability

Ethan is worried because his son Van isn't like other kids. Van doesn't understand many things and can't really talk very well. He's fourteen, but he seems to have the same intellectual capacity of a seven or eight year old. Van might be suffering from an intellectual disability, which used to be called mental retardation.

This is a psychological developmental disorder that is marked by a very low IQ and problems with everyday functioning like communication or taking care of oneself. It is almost always diagnosed before age 18.


Imagine that you are a psychologist and Ethan brings Van to see you. Van is a nice, well-behaved young man and he seems to be relatively happy. So, why does he need to see a psychologist?

Because intellectual disabilities fall under the category of lifespan development disorders, they are covered by the field of psychology. Remember that one of the criteria of intellectual disabilities is a low IQ. IQ is a measure of intellectual ability based on an intelligence test that is administered by a psychologist, another reason why Ethan has brought Van to see you.

The first step in diagnosing Van is to give him an intelligence test. The average IQ is 100, and to have some sort of intellectual disability, Van must score below 70. When you test him, he scores a 59, so he has an intellectual disability. But, there are different levels of disability, so now you must figure out which one Van has.

Mild intellectual disability involves having an IQ between 50 and 69. Usually, people with mild intellectual disabilities take longer to speak and understand, but they can communicate. They can often also take care of themselves. Moderate intellectual disability is diagnosed in patients with an IQ between 35 and 49. These patients usually have trouble communicating and can do some things on their own but are probably not self-sufficient enough to live alone even as an adult.

People with severe intellectual disability have an IQ between 20 and 34. They often have motor difficulties, as well as problems communicating, learning and taking care of themselves. Finally, profound intellectual disability involves having an IQ under 20. People with profound intellectual disabilities are often immobile and cannot take care of themselves. They are not able to communicate. Based on the criteria above, you can diagnose Van with mild intellectual disability.

Causes and Treatment

Ethan is concerned that perhaps it's his fault that Van has an intellectual disability. He's a busy single father, and thinks that maybe he didn't read to Van enough when he was a child or perhaps he didn't give him enough attention. You can reassure Ethan that neither of those things can cause intellectual disabilities. Sometimes, there's no way to know why a person has an intellectual disability, but there are some causes that we know about.

1. Genetics. There are some genes and genetic mutations that can cause intellectual disabilities, such as Down syndrome or Fragile X syndrome.

To unlock this lesson you must be a Member.
Create your account

Additional Activities

Intellectual Disabilities

Activity 1:

For this activity, you are a school psychologist for a group of teenagers who have been diagnosed with mild intellectual disability, thus have an IQ between 50 and 69. You work in a high school and have suggested that group therapy might be a good idea for these adolescents because they all have something in common. During a free period every Friday, eight students come to your office, four boys and four girls. You want to help them come to terms with their mild intellectual disability, as well as help them understand that they have unique strengths. Your goal is for them to feel good about who they are as individuals, develop solid self-esteem, and have positive self-concepts. Write a paper containing three to four paragraphs describing the semester-long intervention you would develop for these young people.

Activity 2:

Some adults with moderate intellectual disabilities, with IQs in the 40s, often can live semi-independent lives with supervision. For example, they can often hold jobs that are repetitive and not complex, and they often live in halfway houses with other adults of a similar intellectual level, under the supervision of an adult caretaker. Make a list of five to ten jobs that might be appropriate for people with moderate intellectual disabilities. What unique issues might you encounter if you were in charge of supervising ten adults with moderate intellectual deficiency in a halfway house?

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account