What Is a Developmental Disability? - Definition & Statistics

Instructor: Chris Clause
In this lesson you will learn to define the term developmental disability, as well as learn about the importance of developmental milestones, common causes, and current prevalence data in the United States. Following completion of this lesson you will have the opportunity to test your knowledge with a short quiz.

Developmental Disabilities Defined

The term developmental disabilities describes any one of a number of conditions that emerge during key developmental periods in childhood which significantly impact a person's physical, cognitive, or behavioral health.

Developmental Milestones

Early childhood is a critical period of rapid physical, cognitive, emotional, and social development. Children are unique individuals, each growing and developing at his or her own pace. While all children don't reach developmental milestones at the same time, researchers have identified specific windows of time within which most healthy children will develop new physical, social, emotional, cognitive, and communication skills. These specific skills, which are thought to occur within a window of time, are referred to as developmental milestones.

As an example, listed below are a few key developmental milestones and the approximate ages at which they are typically reached.

  • By four months of age most babies will start to smile.
  • At nine months of age most babies will start to use their fingers to point to things and will start to copy sounds as a means of communication.
  • Most babies will start walking somewhere around one year of age.
  • By the time most children are two years old they can start to recognize and name items in a picture book.

Awareness of developmental milestones is important in screening for developmental disabilities. For instance, a child who is 20 months old and shows no signs of attempting to walk would likely be screened by a clinician for the possible presence of a developmental disability, since most children attempt to walk sometime around 12 months of age.

Developmental Disability Types

While the term developmental disability may be new to you, the specific conditions which fall under the umbrella heading of developmental disability will likely be more familiar.

Developmental Disability Types
intellectual disability
vision/hearing impairments
cerebral palsy
autism spectrum disorders
attention deficit hyperactivity disorder (ADHD)

The above list is not exhaustive, but as you can see from these examples, the types of developmental disabilities that exist are broad in scope and their impact. Each one of these conditions typically emerges in childhood and has a significant impact on the ability of the child to reach one or more key developmental milestones. The impact on the child's physical, social, emotional, cognitive, and communication skills is significant and long-lasting, usually throughout childhood and oftentimes throughout adulthood as well.

Causes of Developmental Disabilities

Developmental disabilities can be caused by a number of factors, either alone or in combination with one another. These conditions are expressed during key developmental milestones post-birth, but oftentimes the condition originates prior to birth. Certain conditions are the result of genetic factors, other times exposure to toxins is to blame (things such as STDs or drug/alcohol exposure during pregnancy), and sometimes birth injuries can result in a developmental disability.


In 2011 the U.S. Centers for Disease Control and Prevention, along with the Health Resources and Services Administration, published the results of a longitudinal study examining the prevalence of developmental disabilities in the U.S. The data collected during this study represent prevalence rates of developmental disabilities in the U.S. from 1997-2008.

Some of the key findings are as follows.

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

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
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? Study.com 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