The Meridian Public Charter School is a well-regarded institution serving students in preschool through eighth grade on 13th Street between V and W streets in Northwest Washington. Nearly all of its 531 students are black or Hispanic. Eighty-seven percent are from low-income families. The student body’s reading and math proficiency rates are about 15 percentage points above the city average.

But now the school’s record has been tarnished: The Office of the State Superintendent of Education (OSSE, pronounced aw-see) says that teachers or administrators at Meridian likely changed answers on student tests to improve the school’s results.

This is the first D.C. school, traditional public or charter, to be cited by official investigators for cheating based on abnormal numbers of test erasures, changing wrong answers to the correct ones. It’s about time. Until now, investigators hired by OSSE and the D.C. public schools – in addition to the D.C. Inspector General — to probe potential cheating have largely ignored wrong-to-right erasures or accepted school officials’ assurances that the students themselves made the corrections.

Meridian’s chairman, Christopher Siddall, said Wednesday that the school has hired a law firm to determine who was responsible for the erasures. The school also has hired a consulting firm to oversee security during the 2013 D.C. standardized tests underway there this week.

The case against Meridian could cause trouble for other D.C. schools whose student tests have shown wrong-to-right erasures on the same scale or greater than Meridian but who were given a pass.

On April 12, OSSE released a report by the consulting firm Alvarez & Marsal revealing that 11 city schools, including Meridian, had such egregious test security violations on the 2012 D.C. Comprehensive Assessment System exams that many scores were thrown out. At Meridian, all scores were invalidated in five classrooms — a fourth grade and two fifth and sixth grades.

As in previous investigations, Alvarez & Marsal focused on teachers and proctors who defined words and pointed out the right answers to students during exams. It found examples of that behavior at Meridian and other schools, some reported by students. All were declared violations of the District’s test security rules.

But for the first time in any D.C. cheating investigation, the investigators also said that the sheer number of wrong-to-right erasures at Meridian showed “strong circumstantial evidence” that the erasures “occurred at the school level and not at the classroom level.” The erasures themselves violated the city’s rules, the investigators said.

At Meridian, the report said, “1,804 answers were changed from wrong to right,” calling it “one of the highest levels”of such erasures in the city. Meridian had 227 students take the DC-CAS, putting the average number of wrong-to-right erasures per child at about eight. The average per child on the same exams in other D.C. schools was less than one.

In an unusual addition to the report, investigators revealed that four Meridian administrators were questioned extensively about erasures. Meridian administrators “did not offer any potential explanations for the extraordinary level” of wrong-to-right erasures, the report said. “They repeatedly stated that they stood behind the students’ scores,”and each denied changing answers or ordering others to do so.

We don’t know how long cheating has been going on at Meridian unchecked. Seventy percent of its classrooms had wrong-to-right erasure rates that were four standard deviations above the mean in 2009. That climbed to 83 percent in 2010, the second-highest rate in the city. On the 2011 tests, one Meridian classroom registered more than six wrong-to-right erasures per student, yet that year’s investigation, also by Alvarez & Marsal, said Meridian “promotes a culture of compliance and accountability.”

The D.C. Public Charter School Board, which has the power to close the school, plans to discuss the Meridian report next month. The Meridian board could fire the administrators who offered no explanation for tampering.

But that would not go nearly far enough to curb test cheating in city schools. OSSE and DCPS should review several other schools with high rates of wrong-to-right erasures as recently as 2011, including J.O. Wilson Elementary and the Maya Angelou Public Charter middle school. This latest investigation of Meridian should be the model for those to come.