The American Academy of Pediatrics recommends that every child be screened for autism at 18 months and again at 24 months, during routine well-child visits. These two checkpoints are the standard, but screening can happen earlier if parents or pediatricians notice concerning signs, and it can happen much later for children or adults who were missed the first time around.
The Standard Screening Timeline
The 18- and 24-month well-child visits are the two moments when your pediatrician should be running a formal autism-specific screening tool on every child, regardless of whether there are any concerns. This is called universal screening, and it’s separate from the general developmental check-ins that happen at every visit.
The distinction matters. Developmental monitoring is the informal, ongoing process of watching whether your child hits milestones in how they play, speak, move, and interact. Parents, grandparents, and childcare providers all participate in this. Developmental screening is more structured: it uses a standardized questionnaire backed by research and scored against specific thresholds. The CDC recommends broader developmental screening at 9, 18, and 30 months, but the autism-specific screens sit at 18 and 24 months because that age range is where the core social and communication differences of autism become reliably detectable.
What the Screening Actually Looks Like
The most widely used tool is the M-CHAT-R/F (Modified Checklist for Autism in Toddlers, Revised with Follow-Up). It’s validated for children between 16 and 30 months. You, the parent, fill out a questionnaire with 23 yes-or-no items about your child’s behavior. Questions cover things like whether your child makes eye contact, responds to their name, points at objects to share interest, or engages in back-and-forth social play.
A child flags as at risk if they fail two or more of the critical items, or any three items total. If the score is elevated, there’s typically a brief follow-up interview to clarify answers and reduce false positives. A large meta-analysis in JAMA Pediatrics found the tool catches about 83% of children who will later be diagnosed with autism, with a specificity of 99% in the general population. That means it misses some children, but it rarely flags a child who doesn’t have autism. No screening tool is perfect, which is partly why the AAP recommends doing it twice.
Signs That Warrant Earlier Screening
Some behavioral differences can appear as early as 6 to 12 months. None of these are diagnostic on their own, but they’re worth raising with your pediatrician rather than waiting for the 18-month visit:
- Limited response to their name by 12 months
- Reduced babbling, especially the back-and-forth kind that mimics conversation
- Little or no joint attention, which is when a baby and another person share interest in the same thing (looking at a dog together, for example) and both understand the other is paying attention. This typically emerges around 9 months and should be well established by 18 months.
- Few gestures like pointing, waving, or reaching by about 14 months
- Flat or limited facial expressions, including a rare social smile
- Repetitive play patterns, such as spinning wheels on a toy car rather than driving it, or lining objects up
- Preference for playing alone or resistance to physical contact
No single sign means a child has autism. But if you’re noticing several of these patterns together, especially limited eye contact and absent joint attention, that’s a reason to bring it up before the next scheduled screening.
Children With a Sibling on the Spectrum
If your child has an older sibling diagnosed with autism, they’re considered higher risk. The same 18- and 24-month screening schedule applies, but the follow-up process is more direct. Research shows that for these higher-risk siblings, a positive M-CHAT result should lead straight to a developmental evaluation rather than going through the additional follow-up interview step first. The reasoning is simple: the base rate of autism is higher in this group, so a positive screen is more likely to reflect a real concern.
The screening tool’s specificity drops from 99% to about 70% in higher-risk populations, meaning more false positives. But since the cost of missing a diagnosis is high and early intervention makes a measurable difference, clinicians generally err on the side of referring for evaluation.
What Happens After a Positive Screen
A positive screening result is not a diagnosis. It means your child needs a more thorough evaluation. The key principle, emphasized across clinical guidelines, is “do not wait and see.” Delays in follow-up can push back the start of early intervention services during the period when they’re most effective.
After a positive screen, several things typically happen at once. Your pediatrician should refer your child for a diagnostic evaluation, ideally with a team of specialists experienced in autism. This might happen through private providers or a publicly funded early intervention program depending on your child’s age and your insurance situation. For children under three, a referral to your county or state’s Early Intervention Program is standard. For children approaching or past their third birthday, the referral shifts to the local school district’s preschool special education services.
Your child should also get a hearing evaluation. All children with language delays, including those being evaluated for autism, need a formal audiology assessment even if their newborn hearing screening was normal. Hearing problems can mimic some autism-related communication differences, and ruling them out is an important early step. In some cases, depending on the child’s specific developmental profile, a pediatrician may order genetic testing to look for conditions that can co-occur with or resemble autism.
Screening Beyond Toddlerhood
Not every child gets caught by the 18- and 24-month screens. Some children’s traits become more apparent when social demands increase in preschool or elementary school. Others, particularly girls and children who develop strong verbal skills early, may mask differences well enough to slip through early screening.
There’s no single universal screening tool for older children the way the M-CHAT covers toddlers. For school-age children and adolescents, the process usually starts with a parent or teacher raising concerns, followed by a referral for comprehensive diagnostic evaluation. The most widely used diagnostic tools at this stage include structured observation assessments and detailed developmental interviews conducted by psychologists or developmental pediatricians.
For adults who suspect they may be autistic, the path is less standardized. There is no routine adult screening protocol comparable to what exists for toddlers. Adults typically seek evaluation on their own, often after recognizing patterns in themselves or after a child’s diagnosis prompts them to reflect on their own experiences. The diagnostic process for adults relies on clinical interviews, self-report measures, and developmental history, often gathered from parents or other family members who knew the person as a child. A psychologist or psychiatrist with experience in adult autism is the right starting point.