MONTPELIER, Vt. (AP) – It’s every math teacher’s mantra: Check your work.

Apparently, Standard & Poor’s didn’t.

The financial services giant, which analyzed data for U.S. News & World Report’s inaugural ranking of America’s top 100 schools, made a mistake in calculating the score for Montpelier High School and erroneously ranked it the nation’s fifth-best public high school.

Now, the magazine has apologized to the school, saying it’s among the top 500 of 18,000 high schools nationally but not No. 5, as the magazine reported in its “America’s Best High Schools” rankings Dec. 1.

“We feel terrible about having gotten it wrong in the first instance,” said Brian Kelly, the magazine’s editor. “We’re in the business of getting these numbers right. It’s particularly embarrassing that we’re in the business of judging people based on their math scores, and we got our math wrong.”

The magazine based its rankings on performance on standardized tests, performance on the tests by disadvantaged students and the percentage of seniors who took and passed Advanced Placement tests in their high school career.

Therein lies the flub: Twenty eight of the 110 people who graduated last spring did so, not 28 out of a total graduating class of 28, as Standard & Poor’s statisticians calculated.

“We were trying to merge information from the College Board on AP tests taken with information taken from the states or from the National Center for Education Statistics, and we somehow had a very different number,” said statistician Paul Gazzerro, director of analytical criteria for S&P’s School Evaluation Services division.

Somehow, the mistake wasn’t caught.

“It’s the worst nightmare of doing this kind of work,” Gazzerro said.

The error will be acknowledged in the U.S. News & World Report magazine hitting newsstands Dec. 17 and will be fixed in the online rankings, according to Kelly, who wrote a letter of apology to Montpelier school officials Monday.

Turns out it was school officials who ferreted out the mistake and brought it to the magazine’s attention.

“When I realized our ‘readiness index’ of 100 reflected all of our students taking AP and all of them passing, that was the first indication that something wasn’t accurate,” said Principal Peter Evans, who alerted Schools Superintendent Stephen Metcalf.

The school district then asked Standard & Poor’s to explain the discrepancy, and Standard & Poor’s realized the mistake – but asked school officials to delay the announcement until Monday.

“I’m sorry to say that due to a calculation error, the first edition of America’s Best High Schools, published earlier this month by U.S. News & World Report, mistakenly lists Montpelier High School as the fifth best public high school in America,” Kelly told school officials in an e-mail Monday.

At the 396-student school, where the No. 5 ranking had triggered an outpouring of community pride, the reaction was one of disappointment and pride.

Word of the No. 5 ranking had traveled far and wide, eliciting notes of pride from graduates and former residents of Vermont’s capital city. The ranking was prominently displayed on a sign in front.

Cabot Cheese responded by sending a wooden box loaded with samples of its famous cheddar cheese, and townspeople congratulated teachers and school administrators whenever they saw them out and around.

On Monday, there was still pride at having cracked the top 500, but other emotions, too.

Evans ordered a staffer to remove the No. 5 mention from the sign. He went on the public address system to tell the students.

“We were up there among all these schools for the talented and gifted, with special names, and then here we are “Montpelier High School,’ named after our town,” said Nate Ingham, 17, a senior. “It was funny that such a national thing that could be messed up so badly, and that it would happen to us.”

Said Sophia Manley, a 15-year-old sophomore: “When the announcement came on today that they’d screwed up, I didn’t find it too shocking. I don’t really see us as one of the most amazing schools ever, I’d say.”

The silver lining, to some, was that it was the school that blew the whistle on the mistake.

“They did exactly what you’d expect of a first-class institution,” said Kelly. “They didn’t take the number at face value, even though it was in their favor. It shows a great deal of integrity and the kind of standards you’d hope an academic institution will have for itself.”

AP-ES-12-10-07 1735EST