At What Age Can Autism Be Reliably Diagnosed?

When in life can autism be reliably diagnosed? The short answer to that question is generally two years of age or older. Of course, what this means in practice is a bit more complicated.

Autism has been introduced as a spectrum that ranges from “low functioning” to “high functioning.” However, we should not look at autism as a spectrum, and referring to a general “functioning level” can be very overly simplistic.

It is more like a spinning wheel with people falling in different areas of that spinning wheel. There are the foundational behaviors that allow a diagnosis of autism. However, diagnosis (including why and at what age it happens) is different for everyone.

For example, some people are reliably diagnosed with autism at a younger age, then you have people who are diagnosed later in life. At times, such individuals can receive testing even though, based on behaviors, they do not necessarily fall into the autism category.

This article will touch on typical characteristics of autism at any age and dig into the diagnostic process as it relates to age. We’ll also discuss the Waypoints approach to diagnosis and support.

a younger child doing diagnostic testing with a professional

Autism Spectrum Disorder as a Wheel

First, to reiterate, autism spectrum disorder (ASD) is not linear. It is more like a large wheel associated with the following characteristics:

  • Social skills
  • Fixations
  • Routines
  • Sensory issues
  • Stimming
  • Perception
  • Executive functioning
  • Other

Each child can fall anywhere within the wheel experiencing one or more of these characteristics. This might happen when they are a toddler, or it might become apparent later in childhood or into adulthood.

Stages of Autism Diagnosis and a Child’s Development

At times, children display some characteristics or developmental delays prior to the age of two, and screening can help determine if there is a need for an official diagnosis.

Typically, when autism is diagnosed earlier, it helps a child’s development. Being diagnosed by the age of two means the child can move forward with any recommendations to help improve the developmental delays.

According to the CDC, by age two, a diagnosis by an experienced professional can be considered reliable. However, many children do not receive a final diagnosis until much older. Some people are not diagnosed until they are adolescents or adults, thus delay means people with ASD may not get the early help they need.

Let’s look at the stages leading up to an autism diagnosis, specifically developmental monitoring, developmental screening, and developmental diagnosis.

Developmental Monitoring

Before a diagnosis or screening can be determined, you must observe if the child is meeting developmental milestones.

Developmental monitoring is an active process of watching and encouraging conversations between parents and providers about their child’s skills and abilities. Parents, grandparents, early childhood education providers, and other caregivers can participate in developmental monitoring.

Developmental Screening

Next, if family and educators notice some developmental delay, developmental screening takes a closer look. During the phases of life, well-child visits with the child’s pediatrician will also help identify any delay.

If the doctor notices some behaviors, they can recommend testing to determine a reason for delays. The idea is to consider the existence of autistic disorder or any other potential pervasive developmental disorder.

Developmental Diagnosis

The last part leading to an autism diagnosis is a developmental diagnosis. The development diagnosis does not necessarily provide an autism diagnosis, but it can indicate if there is a need for a diagnosis.

A formal evaluation is a more in depth look at the child’s development and uses resources such as the Autism Diagnostic Observation Schedule, Second Edition (ADOS-2) and other assessment tools. It may take up to a month to go through the steps to determine if a diagnosis is necessary.

Early Intervention Is Best for Children and Families

It is important to make sure services and supports are received as early as possible to ensure children can reach their full potential.

We never want to force a diagnosis, but careful observation of developmental milestones and early signs can determine if there is a need. The benefits of an early diagnosis can help the child receive all possible resources, which increase their chances of reaching their full potential.

The Waypoints Approach to Initiating Diagnosis

Waypoints Life monitors behaviors and conducts screenings to determine if there is a need for a diagnosis. If a diagnosis is needed, we conduct an assessment and develop a report to reflect the observations. Finally, we provide recommendations for the next steps.

Within this process, we provide the Autism Diagnostic Interview, Revised (ADI-R) to learn what parents are noticing and what teachers (if the child is in school) are reporting. If there is a need to move forward with an assessment, we schedule an ADOS-2 to observe behaviors reported by the family and school.

After the assessment and speaking with family, school, and others, we design a report to develop a comprehensive plan. From there, we provide recommendations to assist the family with the behaviors displayed during observation.

Waypoints Autism Spectrum Disorders

Waypoints’ process of screening and evaluating results in a solid plan that provides families with structured resources to assist in behaviors and skill development. We work with toddlers as well as older children with ASD.

Please, feel free to explore our site, refer to previous blog posts, and get in touch to learn more and how Waypoints is the best choice for supporting your child’s development.



Screening and diagnosis of autism spectrum disorder. (2022, March 31). Centers for Disease Control and Prevention. Retrieved from

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