“If we could generate accurate estimates of FASD, we’d all benefit,” Dr. Astley said. “But the major limitations in the study design render the results, for the most part, uninterpretable.”

The authors of the study, which was funded by the National Institute on Alcohol Abuse and Alcoholism, acknowledged the study’s limitations and tried to partly compensate by providing a conservative estimate (of 1.1 percent to 5 percent) that is likely low and another estimate (of 3.1 percent to 9.9 percent) that is likely high. Dr. Chambers also said the results might not generalize across the country because although the four communities were diverse, they did not include a large, high-poverty urban area or certain rural or indigenous communities that struggle with high rates of alcoholism.

The locations, which are not named in the publication, include small-to-midsize cities in the Midwest and Rocky Mountains, a Southeast county and a Pacific Coast city the authors identified in interviews as San Diego. Participating first graders were given neurodevelopmental evaluations and most also had their facial features evaluated by dysmorphologists. About 62 percent of the first graders’ mothers were interviewed.

Of 2,962 children evaluated, the researchers identified 222 with a fetal alcohol spectrum disorder, Dr. Chambers said. All but two of them had not been previously diagnosed, although the authors said many parents had been aware their children had learning and behavioral difficulties.

“It’s kind of like the hidden problem,” said Dr. Howard Taras, a study author and professor at the University of California, San Diego, who is the physician for the San Diego Unified School District, which participated in the study. “If not in one classroom, certainly in another, there’s going to be one or two kids with these problems, but they’re not identified as such.”

Identifying children with alcohol-related impairments can help teachers and psychologists work with them more effectively, experts said.

Even if educational approaches might resemble those for other special needs children, the diagnosis tells teachers behavior problems are “not because this child is disobedient, it’s because of some neurological disorder,” said Dr. Svetlana Popova, a senior scientist at the Centre for Addiction and Mental Health’s Institute for Mental Health Policy Research in Toronto, who was a co-author of an editorial about the new study.