Kansas City, Mo. ? A federal judge ended one of the nation’s most litigated school desegregation cases Wednesday after finding the Kansas City school district had made adequate progress in narrowing the achievement gap between black and white students.

U.S. District Judge Dean Whipple, in his decision ending court supervision of the 26-year-old case, said the district was “unlikely to discriminate against African-American children in the future.”

But Arthur A. Benson II, attorney for the plaintiff schoolchildren, said he believed the achievement gap persisted and that he would appeal to the 8th U.S. Circuit Court of Appeals.

“We believe the judge used an improper legal standard to analyze the statistical data concerning the black-white achievement gap,” Benson said.

The achievement gap was the last remaining issue in the case.

A 1997 order by U.S. District Judge Russell G. Clark, who had overseen the case before it was assigned to Whipple, required the district to reduce the test score gap between black and white students by 13 percent in math and reading.

Whipple ruled Wednesday that the district had closed the gap in a majority of categories, but did not have to do so in every grade in both subjects as the plaintiffs had contended.

Whipple also determined that while the district “has not implemented every single requirement” of the court-ordered educational plans, the “vast majority of the requirements have been in place for a substantial period.”

The Kansas City school district was one of a shrinking number of districts with decades-old desegregation cases after several court rulings in the early 1990s provided direction about how such cases should end.

Schoolchildren and the Kansas City district filed the lawsuit in 1977 after voters repeatedly failed to increase taxes to pay for schools. The parties were realigned the next year, with the district named as a defendant and the schoolchildren remaining as plaintiffs.

The lawsuit sought to desegregate the Kansas City school district through an exchange of students from districts on both sides of the Missouri-Kansas line, which runs through the metropolitan area.

At the time, the attempt to involve suburban districts was a fairly unusual approach, said Chris Hansen, a desegregation attorney for the national office of the American Civil Liberties Union in New York.

“The Kansas City case has been one of the most hotly litigated and famous cases in the country,” Hansen said Thursday. “It’s a famous case. It’s been to the Supreme Court several times. … School desegregation lawyers probably don’t know all the cases in the country but you would know Kansas City.”

The case has cost more than $2 billion since 1985.