Ethan Bunkelmann, 6, who has autism, with his mother Ruthie, right, has a moment of frustration while playing Wii. Because he wanders, Ethan wears a wristband with a personal radio frequency located inside. March 28, 2011 Gary Coronado / The Palm Beach Post / ZUMAPRESS

In the first large-scale study of its kind, U.S. and South Korean researchers report that the rate of autism spectrum disorders (ASD) may be significantly higher than previously thought, affecting as many as 1 in 38 children. The findings suggest that many youngsters may be going undiagnosed and untreated for the developmental disorder.

In a study that involved students in both special needs and regular elementary schools in the Ilsan district of Goyang, South Korea, scientists led by Dr. Young Shin Kim at Yale University School of Medicine found that among 55,266 children aged 7 to 12, the rate of ASDs was 2.64% (or one case of ASD for every 38 youngsters). That percentage outstrips the current U.S estimate of 1 in 110 eight-year-olds — around 1% — a rate that has itself risen in recent years.

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The higher rate in South Korea does not mean that autism spectrum disorders are on the rise, the authors say. Rather, it reflects a better estimate of cases based on a more inclusive method of collecting data. “These children didn’t just show up overnight,” Kim says. “They have been there all along. We just didn’t count them.”

In the U.S., the Centers for Disease Control and Prevention (CDC) re-evaluates autism prevalence every two years by looking for autism diagnoses, as well as documented behavioral symptoms typical of the disorder (even without a diagnosis), among a sample of 8% to 10% of the nation’s eight-year-olds. In order to turn around the surveillance data quickly, researchers count only existing cases of ASD or related symptoms noted in the children’s medical records.

Such frequent surveying keeps researchers up-to-date on the changing incidence of autism disorders, say public health officials. But because this method relies on documented cases, it misses children who have not yet been diagnosed, and may underestimate the true prevalence of the condition. “We continue to say with every report from our network that our figures are likely an underestimate,” says Dr. Marshalyn Yeargin-Allsopp, chief of the CDC’s developmental disabilities branch. “We can’t tell you magnitude of the underestimate, but we can tell you that it’s likely an underestimate.”

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Kim set out to figure out exactly how large that gap was. Her group sent a 27-item questionnaire to all of the parents of elementary school children in Ilsan. The questionnaire, which took five minutes to complete, was designed to identify children with any potential social and developmental delays typical of ASD. Once these children were flagged by the screen, they were brought in for further evaluation and possible diagnosis.

By conducting such a broad-based survey of the general population, the scientists likely recorded the most accurate estimate of autism prevalence in school-aged children to date, say experts. Among children enrolled in regular schools — not including those already in special education or disability registries — the researchers found a rate of autism of 1.89%, nearly double the rate in the U.S.

The researchers say they would expect to see similarly high rates of autism emerge in the U.S. and elsewhere if the same data collection strategy were used. “The kids picked up in Korea, many had never been recognized in medical records as having autism,” says Geraldine Dawson, chief science officer for Autism Speaks. “That’s what needs to be done, that kind of broad screening.”

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The findings suggest that many children in mainstream classrooms who are currently having difficultly concentrating or focusing on their lessons may be unknowingly struggling with an autism spectrum disorder. In South Korea, these children — most of whom had a milder form of the disorder, according to the study — may blend into the classroom more easily than they would in the U.S., because classes in Korea are more structured and learning tends to be focused on rote memory. Such rigid lesson plans may actually help autistic children concentrate better and improve their ability to pay attention. “There are few transitions, and the school day doesn’t have many surprises,” Roy Richard Grinker of George Washington University, one of the study’s co-authors, said in a telebriefing with reporters. “Many kids with autism who are doing well can adapt to that highly structured environment and may not be flagged with having any particular problems.”

Still, says Kim, there were a fair number of children in the study who were struggling, if not academically, then socially. “These children in Korea were definitely having difficulties in terms of their social relationships and peer relationships,” she says, noting common problems encountered by children with autism. “They didn’t have friends, they were picked on, and they seemed not to fit in; they weren’t invited by their friends or didn’t participate in many activities outside of school.”

That’s why getting a more accurate reading of the rate of autism in the community is important, says Dawson. Even if children with milder ASD symptoms are able to get by in school, they may face challenges later. “Some children, when they leave school and go to a job interview, or start to interact with other adults, may begin to struggle and need services,” she says.

Early diagnosis and early treatment can help, Dawson says. If children receive behavioral treatments early, it may help reduce or control symptoms and increase their chances of growing up to be independent and functioning adults. Researchers have recently reported success in using brain scans or simple developmental questionnaires to identify the first signs of developmental abnormalities in children as young as age 1.

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Kim stresses that the results of her study shouldn’t alarm parents into thinking that autism has suddenly exploded in schools. “It doesn’t mean there is an increase in new cases,” she says. “We just didn’t know how to find them and diagnose them. Now we know there are kids with social problems who are not being treated, and we know how to help them.”

Although Kim and her colleagues expected to uncover a higher rate of autism by looking for it in a broader population of youngsters, the extent of the increase still came as a surprise. “We knew we were going to have a little higher prevalence than previous studies because we were including a new population in our analysis,” she says. “But to find it in 1.89% of children was a huge surprise to us. We looked at all possibilities to see if we had made an error.”

They had not, but their results will need to be replicated and confirmed by other researchers. Meanwhile, autism experts are already hoping that the same population-based screening method can be applied to American schoolchildren to get a better account of how common autism is in the U.S.

“We have a portfolio of research for our surveillance and research activities,” says Yeargin-Allsopp of the CDC. “This is certainly part of that and is a method we talked about. We realize it can complement what we are currently doing.”

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Such population screens are expensive and labor-intensive. The South Korean study, which was funded by Autism Speaks, the National Institute of Mental Health and several foundations, took five years to complete. But, says Dawson, it’s the best way to figure out the true rate of autism among schoolchildren. “We just don’t know yet in the U.S. how many kids have autism. And we won’t have a good and accurate estimate of that until we use this same approach that includes all children in a population, including those who might not already have received a diagnosis,” she says.

The study is published in the American Journal of Psychiatry.