The Edmonton Public School Board received a failing grade Friday for firing a teacher who broke his school's "no zero" policy.

Lynden Dorval was suspended in 2012 for giving students zeros when they missed tests or didn't hand in assignments. Four months later, he was fired from his position at Ross Sheppard High School.

In Friday's ruling, the Alberta appeal board found that Dorval’s treatment was unfair. There was "no evidence of deliberate misconduct" in Dorval’s grading practices, the board said.

Dorval said he was pleased that the ruling addressed not only his personal situation, but also the concept of the "no zero" policy.

"The Board of Reference was very harsh towards both the principal and the superintendent on the way they handled the situation, very critical of the whole 'no zero' approach," Dorval told CTV Edmonton. "So it was everything I believed in, so I was quite happy to read that."

Dorval is now retired and won't return to teaching. But the appeal board ordered the school board to top up his pension and award him "back pay."

The “no-zero” policy is based on the idea that grades of "zero" can negatively impact student esteem and growth.

A 2009 Alberta Student Assessment Study, commissioned by the provincial government, said that "assessment must not be used to reward or punish" and that "no-zero policies support student-learning outcomes."

In 2013, Ross Sheppard High School reversed its policy, allowing teachers to give zeros when they saw fit.

The Edmonton School Board has 30 days to file an appeal in Dorval's case.

With files from CTV Edmonton and The Canadian Press