WASHINGTON (AP) — A newspaper investigation published Monday questions whether dramatic gains at some D.C. Public Schools, held up as a model for national school reform, were driven by cheating on standardized tests.

Documents obtained by USA Today show some high-scoring schools touted by former Schools Chancellor Michelle Rhee had extraordinarily high numbers of erasures correcting wrong answers. In the story, experts said such erasure rates are so statistically rare that they should have triggered an investigation.

“This is an abnormal pattern,” said Thomas Haladyna, a professor emeritus at Arizona State University who has studied testing for decades.

More than half of D.C. schools had erasure rates that surpassed the city’s averages at least once since 2008, the newspaper found. The erasures are detected by scanners from the city’s testing company, CTB/McGraw-Hill.

At Noyes Elementary, for example, the percentage of fourth-graders rated proficient in math rose from 22 percent to 84 percent between 2007 and 2008. The school was flagged for a high rate of wrong-to-right erasures.

Still, Noyes was named a National Blue Ribbon School by the U.S. Department of Education and was among the schools where Rhee gave teachers and principals $1.5 million in bonuses based on student gains. The principal was later promoted to a higher administrative post.

When former state superintendent Deborah Gist called for an investigation of several schools in 2008, she was rebuffed by Rhee’s staff. Gist left D.C. months later for a similar job in Rhode Island. Her replacement as state superintendent, Kerri Briggs, dropped the request for an investigation.

D.C. Board of Education members said they weren’t told about the extent of testing irregularities.

Schools Chancellor Kaya Henderson, who had been Rhee’s deputy, told USA Today that erasures alone are not evidence of cheating. She said the school system investigated all allegations of testing impropriety.

“In those situations in which evidence of impropriety has been found, we have enforced clear consequences for the staff members involved, without hesitation,” she said, adding that such instances were rare. For most schools, there was no evidence of wrongdoing, she said.

The school system issued a statement Monday, saying it hired an outside firm in 2009 to examine erasure data and followed the firm’s guidance. For this year, the school system said it has implemented stricter protocols for test security.

John Fremer, president of Caveon Consulting Services — the test security firm the city hired in 2009 — told USA Today its investigations were limited. Teachers were asked what they knew about erasures but not whether cheating had taken place. Fremer said D.C. officials did not ask Caveon to perform its own analysis of the test data or work with the testing company to examine each student’s answers to look for any indications of tampering.