Fears that kids will be indoctrinated into an immoral lifestyle is a recurring theme in the many petitions, criticisms and chat boards aimed at the new teaching plan.
It's "a recipe for launching children into a lifestyle of promiscuity ... [that] aims to indoctrinate the next generation," says a lengthy multi-part analysis by the Campaign Life Coalition.
Prominent critic Charles McVety, president of the Institute for Canadian Values, feels the same way.
The curriculum "is a radical ideology," McVety told CBC News. "It is true that 'indoctrination' is sometimes thrown around too lightly, but not in this case."
But education experts say indoctrination isn't that easy, and there's scant evidence sex ed does anything to change a young person's behaviour.
"If you hear anybody on any side of the political spectrum say that sex ed does 'X' behaviorally — that on the right it makes kids have more sex, or on left it makes them use condoms — if they're speaking with great certainty you can pretty much write them off as an ideologue," says Jonathan Zimmerman, a professor of history and education at New York University and author of Too Hot to Handle, a history of sexual education.
"Every side of the spectrum exaggerates both its breadth and its influence," he says.
Attitude and behaviour
For evidence, Zimmerman cites a 2009 study that compared teen pregnancy rates among European countries with different approaches to sexual education.
Progressive Sweden and "appallingly bad" on the education front Italy were among the countries with the fewest pregnancies — suggesting sex ed wasn't a "relevant variable."
Zimmerman says sex ed can influence attitude, but "attitude and behaviour are very different, and it is much harder to influence the latter."
McVety disagrees, and says the power to influence both is "the greatest horror" of Ontario's approach to sex ed.
He feels that the curriculum's controversial section on gender identity threatens to confuse children, and could set them on the road to serious mental health problems.
"If you take little eight year olds … and teach them gender dysphoria, teach them they may not be the gender of their body, you can't tell me that that would have zero impact on all children," he says.
Parents, peers, media
Zimmerman says he's not against sex ed in schools, but suggests people should be realistic about what it can accomplish.
"We should be thinking in broader terms about all the other institutions that educate," he says.
Those institutions include parents, friends and the media.
What's more, until a child is six or seven, parents trump all, says Tracy Vaillancourt, a professor of education and psychology at the University of Ottawa. Ontario's new curriculum will introduce sex ed to children that age in Grade 1.
"The influence of home is greater than the influence of peers or schools" during those early years, she says, adding that religious and political beliefs are "highly influenced by parents."
But as the child grows up, mom and dad lose influence and must share it — mainly with peers and the media.
Faye Mishna, dean and professor of social work at the University of Toronto says that while schools can influence a child's belief system and behaviour — through the curriculum, the climate, the behaviour of teachers and other factors — the notion that they could indoctrinate a student is largely a myth.
"School is influential in many ways," Mishna says, but to accept a belief system without question a child "would have to be pretty cut off from the world."
"You would have to start young and continue probably through adolescence, with little outside influence to balance."
Indoctrination can happen
Vaillancourt says indoctrination does sometimes happen, but it takes effort.
"The individual would need to be getting the same message from many different sources who are perceived to have authority," she says.
Vaillancourt cites the Fundamentalist Church of Jesus Christ of Latter Day Saints, the polygamous splinter group of the Mormons, as an example.
Members of the group in the isolated community of Bountiful, B.C., have been repeatedly investigated by the RCMP over allegations including the trafficking of child brides — leading to polygamy and child-related charges in 2014.
"But keep in mind," Vaillancourt says, that "even with all of the controls in place and scripted dogma, there were still members of that community who did not agree with [the group's] doctrine or practices."
McVety agrees parents are the most important influences during a child's formative years, but maintains schools are a powerful force that, in his view, tend to come out on top. "You can argue whether parents or teachers have greater influence but you can't argue parents and teachers have no influence."
"We always advise parents, with any issue, that you're best off talking to your children beforehand, so that the child is prepared to repel the indoctrination attempts."
"This is common practice but unfortunately … the school wins."