WATCH: Legal challenge over Ontario's sex ed curriculum begins in Toronto

A courtroom in Toronto's Osgoode Hall was packed with lawyers, media, politicians, teachers and students Wednesday morning, as the legal challenge over sex education in Ontario began. 

The two-day hearing includes arguments from lawyers on behalf of the Elementary Teachers Federation of Ontario and the Canadian Civil Liberties Association against those from the education ministry. 

The applicants argue the PC government's decision to repeal the 2015 sex ed curriculum not only removed the ability of teachers to deal with modern issues, but also put in measures to penalize them for diverting from their new curriculum. 

The 2015 version was replaced by one based on the 1998 curriculum, which critics have said doesn't include modern issues such as consent, cyberbullying and gender identity. 

EFTO lawyer Howard Greenblatt argued that had the government simply moved to update the curriculum and made clear that it was a work in progress, the legal challenge probably would not have happened. 

But he said the government's actions constrained the ability of teachers to use free and professional judgement to address modern issues. 

He also took aim at public statements made by politicians including Premier Doug Ford and pointed to a website and phone line that were introduced as a tool for parents to report teachers who didn't abide by the new curriculum. 

When one of the three judges pointed to a factum submitted by the government saying teachers do have flexibility, Greenblatt said that contradicts previous public statements. 

"They're obfuscating," Greenblatt said. 

While the CCLA is arguing the repeal is also a violation of students' Charter rights, the government says the Constitution doesn't entrench on any particular curriculum. 

Before the hearing began, EFTO President Sam Hammond said the current curriculum is "grossly inadequate." 

"It exposes students to increase risk of harm," he said. 

PC MPP Paul Calandra told CP24 that the new curriculum was on firm legal ground. 

"It meets with the Education Act, so we're very confident," he said. "We'll let the case proceed." 

The government also argues that if the previous curriculum didn't break Charter rules, so there's nothing unconstitutional to returning to it. 

With files from the Canadian Press