Screening young children for autism spectrum disorder is becoming very common. The theory goes that early detection can lead to early treatment, which in turn increases the likelihood of a child getting needed services sooner. This is because the younger the brain, the easier it is for it to adapt to changes — and therefore improve with treatment.

Studies have shown that children as young as 18 months could be tested for autism spectrum disorder, but the average age in the U.S. today is around 4 years old. Psychologists at JAMA Pediatrics wanted to find the youngest age a child should be screened.

They looked at more than 1,000 toddlers with and without autism who received their first diagnostic evaluation between 12 and 36 months. They found that while 4 years was too late to accurately confirm a diagnosis of autism,12 months was too early because that is the age kids are beginning to talk, walk and shift their attention.

Between 12 and 16 months, they found, the diagnosis was more reliable than in other age groups. This gives credence to a recommendation from the American Academy of Pediatrics that physicians screen for the condition before a child is 18 months old. In fact, the findings suggested the diagnosis becomes stable starting at 14 months.

The study also pointed out a problem with previous testing. Some of the kids who were identified were initially diagnosed as only having learning disabilities. This means the children were only tested for their learning abilities and not evaluated for whether they showed signs of social delays.

The findings may clear the way for more kids to be reliably tested for autism spectrum disorder, and ensure they get the help they need at the best age for them to begin receiving it.