Charlotte-Mecklenburg Schools are investigating how inflated graduation-track numbers were published in school progress reports, with interim Superintendent Hugh Hattabaugh saying the move damaged the district's credibility.

As of Friday, Hattabaugh said he still didn't know where the false numbers came from or how a team of reviewers failed to flag the error. CMS reports first posted a week ago said more than 98 percent of all high school students were on track to graduate, meaning they had never been held back a grade, even though the same report said only 68 percent were promoted in 2010-11.

On Thursday, after repeated questions from the Observer, CMS said the numbers were wrong and only 75 percent of high school students were on track. The CMS on-time graduation rate was 74 percent last year - a number Hattabaugh said is not in question.

Hattabaugh said he has no reason to believe the numbers were intentionally falsified, but staff is going over all numbers before trying to give the public a corrected version.

"It does create a credibility issue with all data that's posted," Hattabaugh said during a break at a school board retreat. He acknowledged that he did not spot the problem, either.

Louise Woods, a former school board member active in the League of Women Voters, agrees the district's credibility has been hurt: "No one should ever have let that out, because it should be common sense to look at it and say, 'Hey, there's something wrong.' "

Chief Information Officer Scott Muri, who supervises the department that created the report, said Friday he had identified the breakdown in the quality-control process that allowed the bogus numbers to be published. He would not say whether anyone faces disciplinary action, citing personnel confidentiality.

The ability to report accurate data lies at the heart of many CMS functions, from making the pitch for money during a new budget cycle to evaluating student progress and teacher effectiveness. One of the district's biggest goals is increasing the graduation rate.

As part of that push, CMS officials decided to start reporting on the percentage of students "anticipated to graduate on time." Students who have never been held back are counted as on track, because research shows retention, even in the early grades, sharply increases the odds of dropping out.

Muri and Chris Cobitz, the administrator in charge of the data, initially defended the report showing 98 percent of high school students had never been retained, even knowing that high schools have long struggled with high rates of freshman failure, another strong indicator that a student won't graduate.

Cobitz agreed the numbers did not seem realistic but suggested they were based on quirks of timing that could minimize the number of ninth-grade failures tallied, along with that retentions are rare in lower grades.

But after the Observer published a story and asked more questions, Cobitz realized the data sheet he was looking at was different from the numbers CMS put in the reports. He said he does not know where the numbers reported as graduation-track data came from.

The school progress reports were sent to principals about a week and a half before they were released on Tuesday, Muri said. He said he did not know whether any of them raised questions about the on-track numbers, which in some cases diverged wildly from reality. West Charlotte High, which has promotion and graduation rates of just more than 50 percent, was listed as having 95.8 percent of its students on track to graduate on time; the correct number was 53 percent.

At last week's school board meeting, a parent talking about Rocky River High referred to the school being on track to have a 98 percent graduation rate. Hattabaugh and board member Tom Tate said Friday that puzzled them at the time because Rocky River is so new it will have its first graduating class in June.

That number matches the inaccurate one listed on the progress report; the corrected on-track rate for Rocky River is 75 percent.

Online links to the school progress reports were disabled Friday.