Peel Region high school teachers hit the picket lines Monday morning after talks to avert a strike failed.
The Peel District School Board and the Ontario Secondary School Teachers Federationbargained past the midnight strike deadline but were unable to reach an accord.
It means there will be no classes today for the district's 42,000 secondary school students.
Teacher strikes are also ongoing in Rainbow District, encompassing Sudbury and its surrounding regions, and in Durham Region, east of Toronto, where 24,000 students have been kept from class since April 20.
This is the first round of negotiations since the province brought in a new bargaining system, with both local and provincial talks.
Monetary issues are being handled centrally, and the education minister has said it's not clear to her what local issues have prompted the boards to strike.
The province is still trying to hammer out central agreements with both high school and elementary teachers.
Ontario's elementary teachers will be in a legal strike position on May 10.
And Ontario Secondary School Teachers' Federation said Monday that central bargaining with the province and its school board partners had broken down. While no future bargaining dates have been scheduled, the OSSTF said it was ready to resume negotiations at any time.
Central talks between the OSSTF, the province and school boards were previously suspended in mid April, but resumed a few days later.
On another front, some parents are expected to pull their kids from Ontario's schools this week to protest the province's new sex-education curriculum.
A Facebook group is encouraging parents who oppose the sex-ed curriculum to keep their kids home in protest. The group has garnered more than 7,000 "likes," and while some of the messages posted on the page are from outside Ontario, the head of a Toronto-area school board expects the protest will affect classes in her region, at least on Monday.
Toronto District School Board spokeswoman Shari Schwartz-Maltz said it's difficult to determine how many families will participate in the protest.
But Janet McDougald, the chair of the Peel District School Board, said she thinks a "fair number" of parents will pull their kids out of school for at least the first day of the week in the culturally diverse region.
Thousands protested the new sex-ed curriculum, which was previously updated in 1998, on the lawn of the legislature last month and many said they came from communities within Peel Region. But McDougald says there's a lot of misinformation being intentionally circulated about the curriculum.
Under the changes, Grade 3 students will learn about same-sex relationships, kids in Grades 4 and up will learn more about the dangers of online bullying, while the perils of sexting will come in Grade 7.
Lessons about puberty will move from Grade 5 to Grade 4, while masturbation and "gender expression" are mentioned in the Grade 6 curriculum. Anal sex is part of the Grade 7 curriculum, in the context of choosing to abstain from or delay certain activities in order to avoid sexually transmitted infections.
Some opponents of the curriculum say it's not age-appropriate, others insist children should not be taught about same-sex relationships and different gender identities, while still others still wrote on the Facebook group that the curriculum is full of "deviant sexual practices" and amounts to "child abuse."
Premier Kathleen Wynne met privately last week with a group of parents who demanded she withdraw the curriculum. She said it will take effect in September as planned.
Even though education is of provincial jurisdiction, Wynne said she has been warned that the curriculum could be used against the federal Liberals in the upcoming election campaign.
"I have been told that this is something that could be used as a wedge issue," she said recently in Ottawa. "I think that we just need to be aware of that and we need to all be armed with the facts."