The number of D.C. special-education students who are sent to private institutions at taxpayer expense because they can’t be adequately served in public schools has fallen about 20 percent since early 2011, officials say.

The trend has saved money and reduced segregation of kids with disabilities, but has raised concerns that students are being pushed into city schools that aren’t equipped to handle their needs.

Under federal law, students with disabilities must be educated in the “least restrictive environment” — with as much exposure as possible to the general curriculum and a wide range of peers. But students also have a right to go to a private institution if their needs can’t be met in the public schools — which has often been the case in the District’s long-troubled special-education system.

City officials began a concerted effort under then-Mayor Adrian M. Fenty (D) to improve special-education services and bring students with disabilities back into public schools.

That push has continued under Mayor Vincent C. Gray (D), who set a goal of reducing the number of private placements by half — from 2,204 to 1,102 — by the fall of 2014.

The number now stands at about 1,700, according to budget documents and a report Monday in the Washington Examiner. In the 2012-2013 school year, those private placements will cost the city about $109 million — $40 million less than the previous year.

School officials and parents meet each year to determine a child’s annual education plan, including whether a private or public placement is more appropriate.

Gray spokesman Pedro Ribeiro said Monday in an e-mail that children are not returned to public schools unless it’s clear that they’ll receive a “quality educational option equal to or better than their nonpublic placements.”

But advocates worry that there is a financial incentive to return kids to public schools, even when those schools lack an adequate replacement for the specialized services at a private institution.

“Kids with special needs shouldn’t be the cash cow to fix the holes in the District’s budget,” said Judith Sandalow, executive director of the Children’s Law Center, a nonprofit that represents families of students with disabilities.

Sandalow said her organization has seen “quite a number” of students whose needs could not be met by their public school.

As the number of private placements has fallen, the special-education population in the D.C. school system has grown. It is expected to increase by 866 students in 2012-13, to a total of just over 7,800.

Nathaniel Beers, chief of the school system’s Office of Special Education, said every case is weighed according to individual circumstances. But for many kids, he said, a neighborhood school is a better setting than a far-flung private institution.

“When students with disabilities are in public schools, with the appropriate tools and services, they are more likely to graduate with a diploma, they have access to strongly curriculums and they are more apt to succeed in post-secondary opportunities,” Beers said in an e-mail.