What Happens at an Autism Assessment? A Step-by-Step Guide

An autism assessment is a detailed look at how your child communicates, plays, behaves, and develops. A professional or team talks with you about your child’s history, watches and plays with your child, often uses structured tools, and checks for other conditions. It may take one visit or several, and you should then get a written report [1][2].

Before the autism assessment

Most children are referred after a concern at a checkup, a positive screening result, or a report from daycare or school. In the US, your pediatrician may refer you to a developmental-behavioral pediatrician, child psychologist, or autism center. In the UK, a GP, health visitor, or school usually refers your child to the local autism team [3][4].

The team may send questionnaires for you and your child’s teacher or childcare provider, and ask for reports from previous assessments, such as hearing tests or speech therapy. NICE recommends the team gathers reports from preschool or school and results of hearing and vision checks before the assessment [1].

How long will we wait?

Waits vary widely. NICE says an autism assessment should start within 3 months of referral to the autism team [1], but many areas do not meet this. In the US, wait lists for specialist evaluation can also be long [5]. See our guide on who can diagnose autism for ways to reduce delays, and remember that support such as early intervention can start while you wait [2].

What happens during an autism assessment

Every service is a little different, but NICE lists what every assessment should include, and US guidance is similar [1][6]:

1. Talking with you about your child

The clinician asks about your concerns, pregnancy and birth, early milestones, how your child communicates and plays, their behavior at home and in other settings, and family history. Some teams use a structured parent interview, such as the Autism Diagnostic Interview-Revised (ADI-R), which is long and detailed [6]. Others use shorter questionnaires.

2. Observing and playing with your child

A trained clinician plays and talks with your child, often using a structured observation such as the ADOS-2. This uses toys, books, snacks, and games to create natural chances for social communication, like sharing, requesting, and pretend play. The AAP notes the ADOS-2 takes about 30 to 45 minutes and requires intensive training to give and score [6]. You can read more in our guide to the ADOS-2 autism test.

3. Checking development and other skills

The AAP says formal assessment of language, thinking (cognitive) skills, everyday living (adaptive) skills, and sensory responses is an important part of the process [6]. This may involve a psychologist, speech-language pathologist, or occupational therapist. NICE also recommends building a profile of your child’s strengths, skills, and needs [1].

4. A medical check

A doctor reviews your child’s health and does a physical examination, looking for signs of related conditions [1]. They will also think about other explanations for the signs, such as hearing loss, language disorder, intellectual disability, ADHD, anxiety, or the effects of trauma [1].

5. Information from other places

If what you describe and what is seen in clinic do not match, NICE advises gathering more information or observing your child at preschool, school, or home [1]. Children often behave differently in an unfamiliar clinic room.

Medical and genetic tests

Blood tests and scans are not used to diagnose autism. NICE advises against routine medical investigations, but suggests genetic tests or an EEG in particular situations, such as unusual physical features, intellectual disability, or suspected seizures [1]. The AAP recommends offering families genetic testing after diagnosis, starting with chromosomal microarray and fragile X testing, and does not recommend a routine EEG or MRI without a specific reason [6]. A hearing test should be done if it has not been already [2].

How the decision is made

The clinician or team puts together everything they have learned and compares it with the diagnostic criteria in the DSM-5-TR (US) or ICD-11 (UK and elsewhere). NICE is clear that no autism-specific tool should be used alone to diagnose autism [1]. A Cochrane review of diagnostic tools for preschoolers found substantial variation in accuracy, which is why clinical judgment remains central [7].

Sometimes the answer is not clear yet. NICE notes that diagnosis can be uncertain in children under 2, children with a developmental age under 18 months, and children with complex other conditions. In these cases the team may keep your child under review or seek a second opinion [1]. Some services now offer parts of an autism assessment by video. In a trial of 144 toddlers, video-based assessment agreed with a later in-person assessment for 92% of children, and families and clinicians were satisfied with it, though a few autistic children were missed by video [8].

After the autism assessment

NICE recommends that results are shared sensitively, in person, and without delay, even when autism is not diagnosed. You should receive a written report explaining the findings and the reasons for the conclusion, and a follow-up appointment within 6 weeks if your child is diagnosed [1]. The NHS says the report should describe what your child is good at and what they might need help with, as well as any other conditions found [4].

If you disagree with the outcome, ask the team to explain their reasoning. You can ask for a second opinion [4]. Our guide to life after an autism diagnosis covers next steps.

What you can do to prepare

A little preparation helps your child feel safer and helps the team see the full picture. It also means you get more out of the autism assessment.

• Write a short history: milestones, your main worries, and examples of what you see.
• Bring short videos of behaviors that may not show in clinic, such as meltdowns, play, or how your child responds to their name.
• Gather reports from daycare, school, speech therapy, and hearing tests.
• Prepare your child with simple words or pictures about where you are going. Bring favorite snacks, drinks, and comfort items, and plan a calm activity afterward.
• Tell the team about needs in advance, such as sensitivity to noise or bright lights, a need for breaks, or difficulty waiting.
• Write down your questions; see our list of questions to ask at an autism assessment.

When to talk to a professional

If you are waiting for an autism assessment and your child loses skills, has new seizures, or their behavior or sleep suddenly changes, contact your child’s doctor rather than waiting. NICE advises urgent referral for regression in children under 3 [1].

Frequently asked questions

How long does an autism assessment take?

It varies. Some services complete an autism assessment in a single half-day or day, while others spread it across several appointments over weeks. A structured observation like the ADOS-2 takes about 30 to 45 minutes, but the full process includes a detailed history, developmental testing, and a medical check. Ask the service in advance so you can plan for your child.

Can my child be assessed if they don’t talk?

Yes. Assessments are designed for children with all levels of language, including those who do not speak. Tools like the ADOS-2 have modules for children with no words or single words, and clinicians look at gestures, eye contact, play, and how your child shares attention. Language level is also recorded as part of the diagnosis.

Should I stay in the room during the assessment?

Usually yes, especially for young children. For toddlers, parents often join in with play during the observation. For older children, the clinician may spend some time alone with your child. Ask the team beforehand what to expect, and let them know if your child is likely to be very anxious or needs breaks.

What if my child behaves differently on the day?

That is very common and clinicians expect it. Children may be shy, tired, or unusually well behaved in a new place. This is why the history from parents, reports from school or daycare, and your videos matter. If the observation does not match what you see, NICE advises clinicians to gather more information or observe the child in another setting.

References

1. National Institute for Health and Care Excellence. Autism spectrum disorder in under 19s: recognition, referral and diagnosis. Clinical guideline CG128. Published 28 September 2011; last updated 20 December 2017 (minor changes 2021-2025). Link
2. American Academy of Pediatrics Council on Children With Disabilities Autism Subcommittee. If Autism is Suspected, What’s Next? HealthyChildren.org. Last updated April 3, 2025. Link
3. Blitz R, Swoboda S. How Is Autism Diagnosed? HealthyChildren.org (American Academy of Pediatrics). Last updated March 6, 2025. Link
4. NHS. Autism assessments. Page last reviewed 6 May 2026. Link
5. Gordon-Lipkin E, Foster J, Peacock G. Whittling Down the Wait Time: Exploring Models to Minimize the Delay from Initial Concern to Diagnosis and Treatment of Autism Spectrum Disorder. Pediatr Clin North Am. 2016;63(5):851-859. Link
6. Hyman SL, Levy SE, Myers SM; Council on Children With Disabilities, Section on Developmental and Behavioral Pediatrics. Identification, Evaluation, and Management of Children With Autism Spectrum Disorder. Pediatrics. 2020;145(1):e20193447. Link
7. Randall M, Egberts KJ, Samtani A, Scholten RJ, Hooft L, Livingstone N, et al. Diagnostic tests for autism spectrum disorder (ASD) in preschool children. Cochrane Database Syst Rev. 2018;7(7):CD009044. Link
8. Corona LL, Wagner L, Hooper M, Weitlauf A, Foster TE, Hine J, et al. A Randomized Trial of the Accuracy of Novel Telehealth Instruments for the Assessment of Autism in Toddlers. J Autism Dev Disord. 2024;54(6):2069-2080. Link

This guide is general education, not medical advice. Always talk to your child’s doctor or care team. Last checked: October 2026.