CHICAGO | President Bush touted Horace Greeley Elementary on Monday as a school that has thrived under his No Child Left Behind program, despite increasing criticism of the act he sees as one of the signature domestic achievements of his presidency.

Greeley, where 70 percent of students are Hispanic and 92 percent are low-income, was named a Blue Ribbon School under the program in October, one of just 12 public schools in the state to get the distinction and the only one in the Chicago Public Schools system, the nation's third-largest.

"There are things we can do, and must do, by working together," Bush said during his appearance at Greeley, chosen as the backdrop for the president's commemoration of the sixth anniversary of the law's signing.

"I believe the country needs to build upon the successes" of the law, Bush said. "It's not worthwhile to guess when a child's future is at stake."

When NCLB was signed into law six years ago Tuesday, it was hailed as a sweeping bipartisan overhaul of federal education funding by requiring schools to meet certain benchmarks, or adequate yearly progress. But now many education reform advocates and educators say the program has failed to live up to its promise, and even lawmakers who once supported it -- including Sen. Hillary Clinton -- say it needs to be replaced.

Clinton and other Democratic presidential candidates have been batting at NCLB on the campaign trail, criticizing its reliance on standardized test scores. Sen. Barack Obama has said it should be changed "so that we're not just teaching to a test and crowding out programs like art and music."

But Greeley has been making the grade under the program since 2005. It's seen 83 percent of students meeting or exceeding state standards, compared to an average of 64 percent for the entire Chicago Public Schools system.

"In fact, Chicago is an example of NCLB's lack of effectiveness," counters Monty Neill, an NCLB critic and executive director of the National Center for Fair & Open Testing. "The law has failed to raise academic achievement significantly in that city, in other major urban areas or in the nation as a whole."

During his visit Monday, Bush warned Congress that if it doesn't reauthorize NCLB, he will act administratively and unilaterally to make as many changes as he can. He also said if Congress approves a reauthorization, but he considers it to weaken the original law, he would "strongly oppose it and veto it."

Greeley Principal Carlos Azcoitia said part of what sets his school apart is its commitment to bilingual education for all students, including native English speakers. Just more than 30 percent of the students are so-called English language learners -- meaning they primarily speak a language other than English at home.

Greeley qualified for the Blue Ribbon program because its student population has made significant gains over time, Azcoitia said.

Associated Press writer Jennifer Loven contributed to this report.