Definitions of delay and disability
Delays in development are common and about 25% of the population has them. “Delays” refer to weaknesses in one or more areas of development, usually meaning that performance is below average (e.g., less than the 25th percentile, or more often, less than the 16th percentile compared to peers), i.e., that 75% - 84% of same-age children do lots better. While performance around the 16th percentile may not strike you as problematic (it is fine for height, weight, and head circumference), when it comes to school skills, the 16th or even the 25th percentile is not a happy place to be. In a classroom of 25 children, there may be only the one child who is this behind. He or she will quickly notice this and that often leads to frustration, misbehavior and lower self-esteem.

A child with delays will come into kindergarten already behind (e.g., can’t name letters of the alphabet when she sees them). Teachers meanwhile, aim instruction toward the middle of the class, meaning that a child with delays will most likely not understand lots of what is going on. And that’s bad because it means a child with delays isn’t learning much: It is hard to learn from instruction (e.g., sounds of letters) if you don’t have enough prerequisite or background skills (e.g., ability to recognize the shapes of letters when you see them). So…. we want to catch delays early, even in infancy, because if we do, we have a chance of helping a child catch up before he or she gets to school and has a miserable experience. Not all children with delays can catch even with the best of help –sometimes delays progress to disabilities-- but it is worth a try to prevent and intervene early with delays.
Disabilities are conditions that qualify a child for special education services. Usually we are talking about performance below the 5th percentile (meaning that 95% of same age children can do better). About 16% – 18% of the 0 – 18 year-old population has a disability. For adults, this jumps to ~ 22% mostly due to mental health issues. Because there is overlap between disabilities and delays, overall about 22% of our population faces challenges—challenges that are most evident when faced with school tasks.

Most children with disabilities have not only substantive delays in development but also disorders in development. For example, when speaking, they may have words out of order. They may read well but not comprehend what is written. They may recognize common street and store signs but not be able to sound out new words. They may have trouble with the usual sequences of written tasks (e.g., they can't work systematically from top-to-bottom or left-to-right). With articulation skills, they may have difficulty with labial sounds ("m", "b", "p" ) and so substitute other sounds like "g", "k", etc.

Determining that a child is eligible for Early Intervention or  public school special education requires careful evaluation, i.e., much more than a simple screening test). Each State has eligibility requirements that identify the various types of professionals needed, the measures they can use, and the criteria they must apply to various test results before deciding on the type of disability a child has.

Typically, the determination of an exact type of disability is deferred until children are 3 years or older—meaning that, sometimes and confusingly, 0 – 3 year-old children in EI programs are usually referred to as “delayed” even if they have syndromes or other conditions that will likely lead to a disability determination later on.
So what are the various types of disabilities? Which ones are most common? What should we look out for? Not that a screening test should ever be used to make a diagnosis but, it is important to use a screen on which children with the more common disabilities receive a failing score. Too often we focus on motor disorders, which as you can see, in the table below, are tons less frequent than speech-language ones.
Similarly, when we hear the word “disability” we are likely to picture a child with major impairments or syndromes, who look different from most kids. Not so! Only about 15% of all kids with disabilities have an observable syndrome or problem. Disabilities are usually subtle and we need to screen with quality tools if we are to identify children with disabilities.
Both children shown have substantial intellectual deficits. The one on the right lacks dysmorphology and is thus a more typical presentation of developmental delay/disorder/disabilities.
Disabilities by prevalence*
Speech-Language Impairment (e.g., receptive, expressive, and articulation delays and disorders)
~ 17%
Emotional Disturbance (e.g., depression, anxiety, schizophrenia, etc.)
~14% - 21%
Learning Disabilities (e.g., various types of reading, math, or written language problems)
Behavior Disturbance including attention-deficit hyperactivity disorder (children with these conditions may not qualify for special education but often receive help through other public school services).
Intellectual Disabilities (formerly called mental retardation)
~ 1%
Autism Spectrum Disorder
< 1%
Physical Impairment (e.g., cerebral palsy)
< 1/3rd of 1%
Hearing Impairment
~ 1/10th of 1%
Vision Impairment
< 1/10th of 1%
Traumatic Brain Injury
< 1/20th of 1%
Other Health Impairment (e.g., seizure disorders, chronic illness)
< 1/40th of 1%
*Marks K, Glascoe FP, Aylward G, Squires J. Application of Psychometric and Feasibility Core Standards to Developmental-Behavioral Screening Measures in Primary Care Settings. Submitted to Pediatrics, October, 2010.
Please be aware there is much overlap among disabilities because children often have more than one problem, or may acquire additional problems with time. For example, it is hard to be a child with trouble communicating and so it’s not surprising that emotional problems develop (e.g., depression or anxiety), that he or she acts up from frustrations or becomes inattentive (various behavioral issues).  Same goes for children with intellectual delays (they can usually tell that other kids do things much better and find that depressing or anxiety-making. Children with learning disabilities usually notice their poor performance and so may actively avoid overly challenging tasks (e.g., don’t want to go to school; don’t like to read and so don’t get as much practice as others and fall further and further behind). When children don’t understand what is being taught or if they can’t hear or see well enough, they are more likely to space out or fidget (e.g., show signs of attention-deficit hyperactivity disorder). These secondary emotional problems are often called “co-morbidities”.

Also, please be especially alert to the fact that problems with speech-language are:
1.     the most common type of delay or disability;
2.     a main feature of other disabilities too (e.g., autism-spectrum disorder, intellectual disabilities, and sometimes learning disabilities)--Meaning that we must use tools that do a good job of tapping speech-language skills (while not short-shrifting measurement of other domains)
3.     sadly, the least diagnosed of all disabilities. AND even when spotted there is a huge tendency to “defer, defer, defer” rather than “refer, refer, refer”. Wrong and wrong! We need to do better than this—early prevention and intervention work—and that’s the reason we need to screen well, early, and often.
Again, we never diagnose problems from screening tests, but we do want to make sure that when we refer children for additional testing or services, we spell out the possibilities that need exploring (e.g., making sure that children can hear and see, for starters). More on this issue when we get to the section on explaining results and making referrals.

   Delays & Disabilities