People with autism are often described as being "high functioning" or "low functioning," but there are no such official diagnoses. In fact, now that Asperger syndrome, PDD-NOS, and autistic disorder have been removed from the DSM (diagnostic manual) there is only one general category called autism spectrum disorder.﻿﻿

While there are now three levels of autism described in the DSM-5 (Levels 1, 2, and 3), many people use the terms high and low functioning, as they're less clinical. The problem is that the difference between high and low functioning autism can, in many cases, be based on the personal perspectives of a parent, practitioner, or teacher.

What's Wrong with Using the Terms High and Low Functioning Autism?

Is a person high functioning if he's verbal and bright but has such severe sensory challenges that he can't stay in school or hold down a job? Is a person low functioning if she can't use spoken language but is a successful visual artist? The terms can cause miscommunication and confusion because:﻿﻿

Neither term necessarily describes a particular level of intelligence, special talents, anxiety, perseveration, aggression, or sensory challenges.

Neither term provides really useful information about where a person would do best in school. Intelligence is only one measure of whether a child will do well in a general education classroom where issues such as noise, anxiety, and social communication challenges can be overwhelming.

Neither term gives you really useful information about whether a person can function successfully in a public venue. There are people with "low functioning" autism who can sit through and enjoy a movie, for example -- and there are people with "high functioning" autism who find the crowds, smells, sounds, and other sensory challenges to be impossible to manage.

Neither term tells you whether a person is likely to do well in a job. There are people with "low functioning" autism who are happily and gainfully employed, and quite a few people with "high functioning" autism who are not able to find and keep a job they like.

Perhaps most significantly, aggressive behavior, while relatively rare, occurs in autistic people at all levels of severity. Even people with very high functioning autism, who have strong language skills, can "melt down" under certain circumstances.

Defining Autism Based on "Normal" Behaviors and Strengths

Despite problems inherent in the terms high and low functioning autism, they are in common use, usually by people who are not autistic. And they are used to describe the degree to which someone on the spectrum is (or appears to be) similar to people who are NOT on the spectrum.

In other words, autistic people who are or appear to be closer to "normal" are considered to be high functioning. Thus, for example:﻿﻿

High functioning people use spoken language to communicate. Low functioning people are more likely to use technology or picture boards and may have limited or no spoken language.

High functioning people are more likely to be able to manage the expectations of an academic setting. This is often a result of having a better handle on spoken language and a greater awareness of the expectations of others.

High functioning people are usually more aware of social conventions. For example, they are more likely to use tools and utensils typically, greet others appropriately, etc.

Low functioning people generally look and sound very different from their typical peers. In other words, their disability is more visually and aurally obvious to the casual observer. High functioning people are more likely to appear typical (until some event or conversation makes their autism more obvious).

Low functioning people are less likely to be included in typical classes or activities and are more likely to be in a "substantially separate" academic settings. High functioning people are more likely to be included, with or without support, in general classrooms and out-of-school programs.

All of these distinctions, however, are artificial, and they are by no means absolute. That's because autistic people behave differently in different situations, and every individual has a range of strengths and challenges.

While it's handy to describe autistic people based on their similarity to typical people, such descriptions can be misleading. That's because low functioning people may be successful in situations where high functioning people are not, and vice versa.

For example, the "high functioning" person who appears "normal" (or even exceptional) in a college classroom may find it impossible to function at a party. Meanwhile, the "low functioning" person who can't use spoken language to chat may be more than capable of leading a conversation online.

"Levels" of Autism in the DSM-5

To provide some type of differentiation in diagnosis, the DSM-5 (the newest diagnostic manual) now includes three levels of autism based on necessary levels of support. People with level one autism need the least support, while people with level three autism need the most.﻿﻿

While this diagnostic approach sounds logical, it has not proved to be particularly useful. That's in part because the need for support varies for so many reasons. For example, the same individual may need minimal support in the home, significant support at school, and a great deal of support in a novel, unstructured social situation.