Rejecting the findings of a city investigation, an arbitrator has cleared an embattled high school principal of charges that she had allowed students to improperly earn course credits.

Kathleen Elvin was removed from her position as principal of John Dewey High School last July after an investigation by the city Department of Education found that some students earned credit towards graduation simply by completing work packets, without receiving any instruction from teachers.

The findings bolstered critics’ argument that some high schools were boosting their graduation rates by abusing so-called credit recovery programs, which allow students to earn missing credits without retaking entire courses. Chancellor Carmen Fariña called the Dewey findings “disturbing” and said the city had begun the process of firing Elvin.

However, under the department’s supervision, Dewey’s new administration conducted an audit of the credit-recovery program last fall and concluded that students had been properly awarded credits. As a result, the arbitrator ruled that Elvin had been unfairly dismissed, and ordered that she be instated with backpay.

“I was blessed to work at Dewey High School, and I am sad I haven’t been there all this year,” Elvin said at a press conference Tuesday held at the principals union headquarters. She added, “I am living evidence of what character assassination is.”

During Elvin’s two-year tenure as principal at Dewey, the school’s graduation rate rose by 13 points. However, those gains were later cast into doubt by teachers who told investigators that Elvin and other administrators had pressured them to give students credits for classes they failed or never took, and that the school leaders changed students’ grades themselves when teachers refused to.

Critics have long charged that credit-recovery programs allow students to earn credits without learning the material, but defenders say they give struggling students a second chance to graduate. After concerns that the programs were leading to graduation-rate inflation, the city put new limits on the program in 2013.

Following the Dewey investigation last year, officials said that principals and superintendents would receive a training session on the rules around credit accumulation.

Education department spokeswoman Devora Kaye said in a statement Wednesday: “We vigorously sought the termination of Ms. Elvin’s employment. We are disappointed with this decision, and we are continuing to review our options.”