Ron Bradley made the remarks to staff on Aug. 31 during a closed-door meeting at Ross Sheppard High School.
"In my opinion, the culture of the media deteriorated to the quality of pulp fiction and talk radio," Bradley said in a recording leaked to CBC News.
Under Bradley's directive, teachers can't give students zeroes for uncompleted tests or assignments and instead must mark using behaviour codes.
But Ross Sheppard physics teacher Lynden Dorval believes this only makes students unaccountable for their actions.
Dorval was suspended for defying Bradley's directive and faces a termination hearing on Sept. 10.
After Dorval's suspension made national headlines, Edmonton public school trustees agreed to review the district grading practices.
However, Bradley told teachers that they are doing the right thing by following the no-zero directive.
"Everything you did with regard to student achievement and high school completion was the right thing," he said.
"It was aligned with the School Act, board policies and regulations, and they were supported by the board of trustees of Edmonton Public Schools and the superintendent of schools and many, many, many of our colleagues inside and outside the district.
"We are doing the right thing. We are maintaining the high road."
Former teacher also threatened with disciplinary action
Dorval isn't the first teacher to feel pressured because of the policy.
Doug Senuik taught social studies at Ross Sheppard for over two decades.
He says prior to his retirement in June 2011, he received a letter from Bradley warning of disciplinary action if he ignored the policy.
Senuik says since he left the school, he has done his own research on Edmonton schools which have no-zero policies.
He says he's found a large, troubling gap between the marks students receive on their classwork and what they score on provincial exams.
"This system is very easily manipulated," he said.
"You can't call it a policy, it's a theory. It's based on ideology as much as anything, not evidence."
Senuik says he brought his concerns to administrators, as well as the fact that Ontario and Manitoba dropped their own no-zero policies, but was ignored.
He says he didn't speak out publicly about the policy before, but came forward once he heard about the incident with Dorval.
"When a colleague may lose his job, may be terminated based on an experiment, I don't think that's fair. So I think everyone should speak out."