Graduation rates for students with disabilities remain far behind their typically-developing peers, with a new report finding that in some states fewer than half of those in special education earn a diploma.

Nationwide, 64.6 percent of students with disabilities graduated on time in 2014-2015. By comparison, 83.2 percent of all students received diplomas that year.

The disparity is even more striking at the state level, with general education students in 29 states graduating at a rate that is at least 20 percentage points higher than those in special education.

The findings come from the annual GradNation report, which was released Wednesday. The study is produced by Civic Enterprises and the Everyone Graduates Center at the Johns Hopkins University School of Education and is based on federal education data.

Even as the national graduation rate is at an all-time high, the report found that growth has stagnated in many states largely due to lagging progress among students with disabilities as well as black and Hispanic children, English-language learners and those from low-income families.

“In 2015, about half of the country reported high school graduation rates of 85 percent or higher, putting more states on track to reach a 90 percent graduation rate by 2020,” said John Bridgeland, president & CEO of Civic Enterprises and a co-author of the report. “But our country must do more to achieve equity across state lines. It’s time to sharpen our focus on the hardest to reach populations and work to elevate them to success.”

In 33 states, graduation rates for students in special education were below 70 percent, according to the analysis. Fewer than half of such students graduated in South Carolina, Louisiana, Mississippi and Nevada.

The report indicated that most students receiving special education services are diagnosed with a specific learning disability, a speech or language impairment or other health impairment like attention deficit hyperactivity disorder, epilepsy or Tourette syndrome.

“These students, and so many others who are identified with a disability, can meet regular diploma requirements with the right supports in place,” the authors wrote.