A federal appeals court on Friday ruled that the D.C. government is not doing enough to find and assist young children with special needs who have not yet entered the school system.

In a 3-0 ruling, the court upheld an earlier decision that found a “persistent failure” by city officials to provide services for some of the city’s most vulnerable children and their families.

The long-running case began in 2005 when parents of six children, ages 3 to 6, sued the District of Columbia, alleging that the city failed to meet the requirements of the federal Individuals with Disabilities Education Act. A provision of that law called “Child Find” holds school districts responsible for reaching out and locating young children with disabilities and developmental delays and providing services and programs for them so that they can more easily transition into kindergarten and elementary school.

In 2011, U.S. District Court Judge Royce C. Lamberth ruled in favor of the plaintiffs in DL v. District of Columbia, saying that District officials’ “persistent failure to live up to their statutory obligations, a failure that works a severe and lasting harm on one of society’s most vulnerable populations — disabled preschool children — is deeply troubling to the court.”

Lamberth ordered the city to ensure that at least 8.5 percent of District residents between the age of 3 and 5 receive special-education services. Earlier court findings had shown the city was regularly failing to identify between 98 and 515 children a month with disabilities and had the lowest percentage of special education enrollment in the United States. In the 2014-15 school year, the city provided special education and related services to 6.2 percent of the city’s 3- to 5-year-olds, District officials reported. The early intervention programs in the District are run by the Office of the State Superintendent of Education (OSSE), and the preschool programs are run by the D.C. Public Schools.

Last year, after the case was returned to him, Lamberth again ruled in favor of the plaintiffs, saying “The District’s lack of effective Child Find and transition poli­cies is particularly troubling in light of the intense scrutiny and seemingly constant admonishment it has received over the last decade.”

In its most recent appeal, the D.C. government argued the case was moot because the original named plaintiffs were now over 5 years old and the class action certification of the lawsuit was improper. The District also questioned the federal government’s jurisdiction over how the program was run.

But the court disagreed with the District, saying its position “would eviscerate the very purpose of IDEA” which was intended to make school districts proactive in identifying students with disabilities.

“The District, which has enthusiastically accepted millions of dollars in IDEA funding, now proposes to shift that burden back to the parents,” the court said in the ruling authored by Judge David S. Tatel, who was joined by Judge Thomas B. Griffith and Judge Patricia A. Millett.

In rejecting the District’s argument, the court said: “In the District’s view, it would be up to each and every parent, many of whom are poor, homeless, and perhaps disabled themselves, to somehow determine whether their children are eligible for special education services and then to retain counsel to sue the District to obtain the services to which they are entitled. Given the purpose of IDEA, we cannot imagine a more preposterous argument.”

A spokesman for D.C. Attorney General Karl A. Racine did not immediately respond to a request for comment on the decision.

The ruling is a victory for children with disabilities, said Judith Sandalow, executive director of the Childrens Law Center. “Fundamentally it clears away a hurdle in the legal battle to get this city to properly identify and provide services to toddlers,” she said. “The earlier we identify the more we can do to make sure that they are still able to learn along with their typically developing peers. The longer we wait, the harder it is to do.”

Ann E. Marimow contributed to this report.