It’s recommended that all young children be regularly screened for developmental delays, but new research finds that’s not happening with fewer than 1 in 5 kids in some areas being evaluated.

Nationally, less than a third of those ages 9 to 35 months received developmental screening, according to findings published online this week in the journal JAMA Pediatrics.

The study looked at data collected through the 2016 National Survey of Children’s Health, a government survey of more than 50,000 U.S. adults asking about children in their households under age 18.

Parents were asked if a doctor or other health care provider had inquired about developmental concerns — a process known as developmental surveillance — or if they were asked to fill out a questionnaire about developmental concerns, which is considered screening.

The American Academy of Pediatrics recommends that all children receive developmental surveillance at every health visit and that developmental screening be conducted at 9, 18 and 30 months or any time a concern is raised.

Nonetheless, the study found just 30.4 percent of kids in the target age group had been screened in the previous year, while 37.1 percent had participated in surveillance. More than half of children had received neither.

And the numbers varied substantially by state. At the low end, only 17.2 percent of Mississippi children were screened compared to a high of 58.8 percent in Oregon.

One factor that did appear to influence if children received screening or surveillance was whether they had a regular source for medical care, the study found.

Despite the geographic variation, it is possible to improve screening rates in a meaningful way, according to Christina Bethell of the Johns Hopkins Bloomberg School of Public Health who worked on the study.

Oregon had one of the lowest screening rates in 2007 and now leads the nation, she said. One reason may be that the state implemented incentives to improve quality through a Medicaid demonstration waiver, a tactic that could work in other places, Bethell indicated.

“We need to create comprehensive systems to optimize early child development in the first 1,000 days of life, which we know is dramatically important for child and population health,” Bethell said. “Even in the best states, only about half of children are receiving screening and surveillance. We still have a long way to go.”