Nationwide, about 13 percent of students qualify for services under the Individuals with Disabilities Education Act. But that number varies significantly from one state to the next, government investigators say.

At the low end, 6.4 percent of school children ages 6 to 21 in one state were served under IDEA in the fall of 2016 compared to a high of 15.1 percent in another.

Those are the findings of a Government Accountability Office report out this week.

For the report, investigators looked at federal data on special education from 2011 to 2016, examined guidance and other documents as well as relevant laws and interviewed stakeholders in four states — Colorado, Iowa, Massachusetts and New York — with varying percentages of students served.

Under IDEA’s “child find” mandate, states must have practices in place to ensure that they identify, locate and evaluate all children with disabilities.

“IDEA gives states some latitude in setting eligibility criteria and defining disability categories. In addition, states may determine their own processes for identifying and evaluating children,” the report indicated. “As a result, a child eligible for services in one state might be ineligible in another.”

Several issues could be contributing to discrepancies between states, GAO found, including difficulty getting referrals from parents or physicians, limited availability of staff qualified to conduct evaluations and confusion among educators about when special education services are appropriate.

Meanwhile, investigators noted that the Department of Education, which is tasked with oversight, relies on data and information that states submit annually to assess if states are meeting their “child find” obligation under IDEA.

“The GAO’s report reveals how the combination of inconsistent state policies and inadequate federal oversight continues to allow thousands of young people with disabilities to fall through the cracks,” said U.S. Rep. Bobby Scott, D-Va., who chairs the House education committee and was one of the lawmakers who requested the report. “The Department of Education must hold states accountable for complying with federal law, so that all children, infants and toddlers with disabilities are getting the services and support they need to receive a meaningful educational benefit, so that they can reach their full potential.”

GAO noted that media reports in recent years have prompted concerns about how well states are fulfilling their “child find” obligation. Most notably, a 2016 Houston Chronicle investigation alleged that Texas set an arbitrary cap of 8.5 percent for special education enrollment in that state.