About 1 in 31 children in the United States are diagnosed with autism spectrum disorder, and most parents first notice something is different well before a formal evaluation happens. The signs vary widely depending on your child’s age, sex, and where they fall on the spectrum, but certain patterns in social communication, repetitive behavior, and sensory responses show up consistently. Knowing what to look for at each stage can help you move from “something feels off” to a clear answer.
Early Signs in Babies and Young Toddlers
Some signs of autism are visible before a child’s first birthday, though they’re easy to miss because babies develop at different rates. The clearest early red flags involve how your baby connects with you socially. A baby at risk for autism may not use eye contact the way other infants do, sometimes actively turning away, pushing away, or closing their eyes rather than meeting your gaze. When you call their name, even repeatedly, they may not look toward you. Typically developing babies turn toward a familiar voice reliably by around 9 months.
Joint attention is one of the most telling early markers. This is the natural impulse to share focus on something with another person. If you point across the room at a toy or shift your gaze toward something interesting, most babies will follow your eyes or your finger. A child at risk for autism often won’t. Similarly, they may not hold up objects to show you something exciting. They might hand you a toy when they need help opening it, but without the eye contact or vocalizations that signal “look at this cool thing.”
Another pattern to watch for: limited shared enjoyment. During games like peekaboo, a child at risk may not smile, laugh, make eye contact, or clap along. They might enjoy their own actions, like spinning a toy, but not light up during back-and-forth play with you.
What Shows Up Between 18 and 36 Months
The toddler years are when most parents first feel certain something is going on. Language delays are common, but autism-related communication differences go beyond late talking. Your child might echo words or phrases they’ve heard (from you, from TV) without using them meaningfully. They might not point to things they want, instead pulling your hand toward an object like a tool. Some toddlers develop a few words and then lose them, which can be alarming.
That loss of skills, called developmental regression, happens in roughly one-third of young children with autism. It most commonly occurs around 20 months of age, though it can happen anywhere from the second year of life into preschool. Children typically lose speech first, but some also lose social skills, nonverbal communication, or the ability to play the way they used to. If your toddler was waving, babbling, or saying words and then stops, that warrants prompt attention.
Repetitive behaviors often become more noticeable at this age too. Your child might line up toys in precise rows, spin wheels for long stretches, flip objects over and over, or develop rigid routines around food, walking routes, or daily sequences. Small changes to those routines, like taking a different path to daycare, may trigger intense distress that seems out of proportion.
Signs in School-Age Children
Some children aren’t identified until they enter school, where the social demands become more complex. A child who seemed quiet or quirky at home may struggle visibly when they need to navigate group play, take turns in conversation, or read the unspoken rules of a classroom. They may talk at length about a narrow interest without noticing that the other child has lost interest. They might take figures of speech literally, missing sarcasm, jokes, or implied meaning.
Friendships can be particularly difficult. Your child might want friends but not know how to make or keep them, or they might seem genuinely uninterested in peers and prefer solitary activities. Difficulty adjusting their behavior to different social settings is another hallmark: they may interact the same way with a teacher as with a classmate, not picking up on the social cues that signal different expectations.
Sensory differences also become more apparent in structured environments. Some children are overwhelmed by fluorescent lights, cafeteria noise, or the texture of certain clothing. Others seem unusually indifferent to pain or temperature. A child might excessively smell or touch objects, or become fascinated by lights and movement in ways their peers don’t.
Self-Stimulatory Behavior
Stimming, short for self-stimulatory behavior, is one of the most recognizable features of autism, though it exists on a spectrum of its own. Common examples include hand flapping, body rocking, pacing, and repeating words or sounds. Some children tap surfaces, twist their fingers near their eyes, or chew on objects. These behaviors typically serve a purpose: they help the child regulate sensory input, manage anxiety, or express excitement. Stimming alone doesn’t mean a child has autism (many children stim occasionally), but frequent, intense, or varied stimming alongside social communication differences is a meaningful pattern.
Why Girls Are Often Missed
Autism is diagnosed about 3.4 times more often in boys than in girls, but a growing body of evidence suggests that gap partly reflects missed diagnoses in girls rather than a true difference in prevalence. Girls with autism tend to show better conversational skills, more natural-looking nonverbal communication, and fewer obvious repetitive behaviors compared to boys with similar levels of autism traits. On formal diagnostic assessments, autistic girls may score similarly to autistic boys, yet in everyday life they appear more socially capable because they’ve learned to camouflage.
This camouflaging involves masking (hiding autistic traits), compensation (deliberately performing “non-autistic” social behaviors), and assimilation (working hard to fit in). Research using the Camouflaging Autistic Traits Questionnaire consistently shows that females score higher on all three. The cost is real: girls who mask tend to internalize their difficulties, showing up as anxiety, depression, or emotional exhaustion rather than the externalizing behaviors clinicians typically associate with autism. If your daughter seems to hold it together at school but melts down at home, has one or two close friendships she maintains through intense effort, or mirrors other girls’ social behavior without seeming to genuinely understand it, these are patterns worth exploring.
How Screening and Diagnosis Work
The path from concern to diagnosis typically moves through three stages: monitoring, screening, and formal evaluation.
Developmental monitoring happens at every well-child visit. It’s the informal process of tracking milestones and talking with your pediatrician about what your child is and isn’t doing. If something seems off, the next step is a formal screening. The American Academy of Pediatrics recommends general developmental screening at 9, 18, and 30 months, plus autism-specific screening at 18 and 24 months. The most widely used tool is the M-CHAT-R/F, a parent questionnaire that takes about five minutes. Scores of 0 to 2 indicate low risk. Scores of 3 to 7 put a child in the medium-risk range and trigger follow-up questions. A score of 8 to 20 is considered high risk and warrants immediate referral. Children who score 3 or higher initially and 2 or higher on follow-up have roughly a 48% chance of receiving an ASD diagnosis.
A screening isn’t a diagnosis. If the screening flags a concern, your child will be referred for a formal developmental evaluation. This involves one or more specialists, typically a developmental pediatrician, child psychologist, speech-language pathologist, or occupational therapist. They observe your child, test specific skills, interview you about your child’s history, and compare what they find against the diagnostic criteria. You don’t need to wait for your pediatrician to suggest screening. If you have concerns at any age, you can request one.
What Clinicians Are Looking For
A formal autism diagnosis requires two things. First, your child must show persistent difficulties in all three areas of social communication: back-and-forth social interaction, nonverbal communication (eye contact, gestures, facial expressions), and building and maintaining relationships. Second, they must show at least two of four types of repetitive or restricted behaviors: repetitive movements, speech, or use of objects; rigid insistence on routines or sameness; intensely focused interests; or unusual sensory responses.
These patterns need to be present from early childhood, even if they aren’t fully recognized until later, and they need to meaningfully affect daily life. A child who is simply introverted or a late talker won’t meet these criteria. The diagnosis captures a specific combination of social communication differences and behavioral patterns that together create a distinct developmental profile.
Trust What You’re Noticing
Parents are often the first to sense that something is different about their child’s development. If you’re reading this article, you’ve probably already noticed patterns that prompted the search. The most useful thing you can do right now is write down the specific behaviors you’re seeing, when they started, and how often they happen. That list becomes invaluable when you talk to your pediatrician or request a screening. Early identification leads to earlier support, and children who receive intervention during the toddler and preschool years consistently show better outcomes in communication, social skills, and adaptive behavior than those identified later.