WASHINGTON — Anointing themselves the “odd couple,” New York City’s schools chancellor, Joel Klein, and the Reverend Al Sharpton are teaming up to confront what they call the nation’s most urgent civil rights issue: the educational achievement gap between white and minority students.

The unlikely pairing of schools chief and activist appeared here yesterday with national education leaders to launch a coalition aimed at pressuring the presidential candidates to address racial disparities that persist in classrooms across the country.

Pointing to statistics that show black and Hispanic students lagging far behind their white counterparts in test scores and graduation rates, Mr. Klein said the achievement gap had “barely narrowed” in the more than five decades since the Supreme Court ordered the desegregation of the schools in the landmark 1954 decision, Brown v. Board of Education.

“In my view, that gap is the shame of this great nation,” the chancellor said in announcing the venture, called the Education Equality Project, at the National Press Club.

Black and Hispanic high school students are on average four years behind white students in math and reading skills, data show. Just 55% of black students graduated on time in 2005 across the nation, compared to 78% of white students, according to a recent report by the Editorial Projects in Education Research Center.

“We’re in an age where we’re trying to move beyond race. The achievement in education is not beyond race,” Rev. Sharpton said.

Mr. Klein hailed Rev. Sharpton as a “civil rights champion,” pledging to work with him despite their differences on some issues. Quoting the movie “Casablanca,” Mr. Klein told him: “I think this is the beginning of a beautiful friendship.”

While Rev. Sharpton criticized Mr. Klein as recently as last year over contracting for the schools, he has not been as vocal as other black leaders in the city, including the local NAACP, in denouncing Mr. Klein’s stewardship of the Department of Education.

Advocates yesterday said Rev. Sharpton’s decision to partner with the chancellor was striking and could signal a break with the unions, which have long been seen as resistant to systemic change.

“It’s not everyday that someone like Rev. Sharpton is willing to stand up and talk about the extent of the problem,” the executive director of the New York-based Democrats for Education Reform, Joseph Williams, who also joined the new coalition yesterday, said. “Essentially he’s saying there are no sacred cows.”

Rev. Sharpton offered hints of a shift yesterday, although he did not directly criticize the unions.

“Our children are drowning in the waters of indifference and old coalitions that no longer work and no longer care,” he said.

The coalition did not offer specific recommendations or a detailed policy agenda, but Mr. Klein said they would emphasize improving teacher quality, accountability, increased parental involvement, and making charter schools “viable” throughout the country. The group plans to hold forums at both the Republican and Democratic national conventions this summer.

Mr. Klein and other coalition members signaled a willingness to confront entrenched policies like teacher tenure, even if it meant a conflict with unions. “We will take on laws, contracts, and other barriers to successfully educating our children,” Mr. Klein said.

The chancellor of the Washington, D.C., school system, Michelle Rhee, was more blunt: “We are finally going to put aside the rights and privileges and priorities of adults” — and return the focus to children, she said.

Also appearing at the announcement yesterday was a former Colorado governor and superintendent of the Los Angeles school system, Roy Romer, and the head of the Baltimore schools, Andres Alonso.

The president of the city’s United Federation of Teachers, Randi Weingarten, warned Mr. Klein and his new coalition against taking a confrontational approach. “If he is using words that kind of demonize teachers again, that would be very sad,” she said in an interview. “The times he has worked with us and worked with teachers, he has succeeded.”

Ms. Weingarten said it was “highly ironic” that he would be in Washington to push a national education agenda while the Bloomberg administration is proposing budget cuts for schools in the five boroughs.

She had kind words for Rev. Sharpton, but she suggested he was new to the battle for education equality. “There are some of us who have toiled in this fight for a very long time,” Ms. Weingarten said. She added: “I welcome Al Sharpton onto this achievement bus. I think it’s terrific.”