More teachers at Edmonton's Ross Sheppard high school are speaking out against a "no zero" grading policy that led to a defiant colleague losing his job, but the principal of the school still stands by the marking system.

Teachers who believe the policy is misguided told CBC News their students are getting a free ride and are consequently losing out on getting adequate preparation for post-secondary education.

Lynden Dorval, a physics teacher at Ross Sheppard High School, was fired earlier this month. (CBC)

"It's so disheartening that these kids are getting a false impression as to what their abilities are," one educator at the school said. "It's not fair to them and it's not fair to the parents."

Of the three teachers who spoke with CBC News, none wished to provide their names out of fear they could be fired.

Former Ross Sheppard teacher Lynden Dorval was sacked earlier this month, partly due to him giving out zeros to students, despite a directive from the administration.

Ron Bradley, the principal at Ross Sheppard, explained that the controversial grading system assigns behaviour "codes" instead of zero marks to pupils who fail to hand in work, but he sought to clarify that a zero grade is still possible if the problem persists.

'We hold them accountable,' superintendent says

"We will, in fact, record behaviours using codes in the first instance," Bradley told CBC News. "As we go through a series of interventions, we may, in fact, award a zero at the end."

On Friday, Edmonton Public Schools superintendent Edgar Schmidt issued a letter to parents assuring them their children were being graded wisely.

The letter stated that "when students don't do their work, we hold them accountable" and that the school board has not "and will not pass students who do not complete their course requirements."

But the teachers who spoke anonymously with CBC News disagreed.

"That statement is a lie," one teacher said. "Because they essentially forgive the missing stuff, the mark is inflated and as a result of that, the students pass."

Discussions about the grading system are expected to continue Tuesday, when the first parent council meeting of the year is held as well as a school board trustees meeting.