A fifth-grade teacher at a District public school allegedly stole a peek at part of a high-stakes standardized exam in April and used that peek to create an illicit study guide for her students so they’d perform well.

The incident at Plummer Elementary in Southeast Washington, disclosed here for the first time, led the school system to place Principal Christopher Gray on leave while an investigation is underway.

Gray, who has led Plummer for nine years, denies wrongdoing and fears that he is being made a scapegoat.

But the school system is right to be wary, given the school’s record. Plummer was one of four District schools where suspected cheating was reported during last year’s D.C. Comprehensive Assessment System exams.

The teacher will be terminated soon, when necessary paperwork is completed, according to a person with knowledge of the incident. The teacher said in a brief telephone interview that the allegations are not true.

“I can confirm that there is an instance of cheating at Plummer on the D.C. CAS [exam], and we have taken personnel action accordingly,” D.C. Public Schools spokeswoman Melissa Salmanowitz said.

In one sense, the cheating is a disappointing reminder of one of the costs of contemporary education reform. The emphasis on using standardized tests to hold teachers and principals accountable has inevitably increased the pressure on educators to break the rules.

Under the system introduced in the District by former chancellor Michelle Rhee, standardized tests play a bigger role in determining teachers’ evaluations and bonuses.

This gives teachers an incentive to cheat.

I’m not excusing it. I’m just explaining.

Moreover, it’s not clear that the tests work. A new, large-scale study released Tuesday found little or no correlation between quality teaching and teachers’ appraisals based partly on student test scores.

In another sense, however, it’s heartening that DCPS moved quickly against the apparent perpetrator. That’s an improvement from the Rhee era, when administrators seemed slow to respond to cheating allegations for fear of discrediting the reform agenda.

Salmanowitz praised the people at Plummer who went up the chain of command with suspicions about the illicit study guide.

“In this instance, we are pleased to see that the safeguards and protocols that we have in place work,” she said. “We commend the staff that were courageous enough to report concerns.”

The incident began April 1, the first day of CAS testing at Plummer.

After a student handed in a test early, having completed the math portion conducted that day, the teacher took the booklet aside. She wrote notes while reviewing the reading portion to be administered two days later, according to three people familiar with the incident.

The next day, the teacher handed out a two-page study guide based on her sneak peek of the reading exam — which teachers as well as students are forbidden to see in advance.

She didn’t get away with it.

Others at Plummer reported the suspicious study guide on the day it was handed out. The teacher was put on administrative leave that evening, although she later returned to work pending disciplinary action.

The students’ test results will be invalidated.

The teacher denied wrongdoing in a short conversation with me. But she reportedly admitted the offense when school system authorities questioned her, according to the people familiar with the school, who spoke on the condition of anonymity because they were not authorized to speak publicly.

Gray, the principal, was put on leave Monday. He has not been formally accused of anything but suggested in telephone interviews that authorities suspect him of trying to conceal testing irregularities.

He said he was not given a reason for being put on leave after what he described as hostile questioning from DCPS officials.

“I feel like I am becoming the scapegoat in the situation when I have done nothing wrong and had no part in this cheating incident,” Gray said. “I did not do anything to attempt to cover up any cheating.”

Gray also said he had “absolutely no involvement” with last year’s cheating incident. He said he reported the recent one as soon as he heard about it.

“Once the incident of possible cheating was brought to my attention, I immediately followed DCPS protocol and notified my supervisor and contacted the DCPS central office,” Gray said.

The principal shouldn’t take a fall for the sake of public relations. But DCPS needs to pursue this fully and to the end, and it deserves praise for its aggressive first response.

For previous columns, go to washingtonpost.com/mccartney.