This story is part of School Violence, a CBC News series examining the impact of peer-on-peer violence on students and parents. WARNING: This story contains graphic language and video.

Stepping off the grounds of their high school, those with cellphones out, filming, knew what was about to happen. But the Grade 9 student in Windsor, Ont., into his first days of a new school year, did not.

It happened quickly on Sept. 12 of last year. An older boy approached Jayden Trudell, 15, from behind and blind-sided him with a hard punch to the head.

Jayden was then picked up and dropped, his head slammed into the pavement. As the video shows, he did not move. Yet the assault continued, with kicks and punches.

"His neck was bent in a weird way, so I thought he was dead," his cousin, Jaxson Da Silva-Trudell, recalled of the attack. "I thought Jayden died right then and there."

Jayden was rushed to hospital in critical condition and spent months recovering from a fractured skull, a brain bleed and hearing damage. His attackers were expelled, charged and ultimately convicted of assault.

Jaxson Da Silva-Trudell said he thought his cousin Jayden had died after he was violently attacked steps away from his high school last September. Jaxson jumped in to help and has since experienced threats himself. (Caitlin Taylor/CBC)

"No one knew at the time if Jayden was gonna live or die," said his grandfather, Kevin Trudell, a retired police officer. The approach of investigators at the scene, he said, was indicative of the seriousness of the assault.

"They treated it as a murder scene. It was [like] a murder investigation."

Jayden's case may seem like an egregious example, but violence in Canadian schools appears to be rife when you ask students directly about peer-on-peer behaviour at school.

WARNING: This video may be disturbing to some viewers:

This viral video shows a 14-year-old being sucker-punched by a larger male teen from behind. The attacker proceeds to pick up the victim and slam him into the cement head first. 1:28

According to a survey conducted by Mission Research for CBC News, more than one-third of students between the ages of 14 and 21 say they were physically assaulted at least once before reaching high school.

Boys are even more likely to face violence, with four in 10 boys between the ages of 14 and 21 reporting they were on the receiving end of an assault involving slaps, punches, kicks or bites.

In high school, one in five boys surveyed say they were threatened with a weapon.

Watch the full Marketplace investigation at 8 p.m. Friday on CBC TV or online.

It's a sombre statistic that turned deadly last month at a Hamilton high school.

Just a month into Grade 9, 14-year-old Devan Bracci-Selvey was fatally stabbed while on school property. It reportedly came after weeks of his family pleading with school officials to confront bullying at the hands of other students.

In a tearful and angry statement after her son's death, Shari-Ann Bracci-Selvey said "everyone failed my son."

Two students have since been charged with his murder.

Survey reveals school violence varies by region

While the Greater Toronto Area is home to Canada's greatest number of students, the survey also reveals significantly higher rates of violence in its high schools compared to other regions in Ontario and across the country.

Students in Quebec, meanwhile, reported the lowest incidence of experiencing violence at the hands of another student.

The Prairies stood out for reports of unwanted sexual contact, such as inappropriate touching or grabbing, with one in four saying they have experienced it. An even higher number — nearly one in three — have experienced peers sharing a sexual rumour or message about them with others at least once, significantly higher than the national average.

School violence turned deadly earlier this month outside Sir Winston Churchill Secondary School in Hamilton, where 14-year-old Devan Bracci-Selvey was fatally stabbed. Two people have been charged with first-degree murder. (Dan Taekema/CBC)

CBC News asked school boards and education officials across Canada to release their own records on violent incidents. Many refused or placed significant roadblocks in the way of accessing the information, including demands for hundreds of dollars in order to process the request. One board worried the release of such records might cause "reputational risk" to its individual schools.

Faced with those barriers, CBC decided to go to the students directly, commissioning a survey of more than 4,000 young people.

"You first have to be able to identify what the problem is — understand how serious it is, how many people are affected by it — and then move forward with a plan to fix it," said Tracy Vaillancourt, a violence prevention expert at the University of Ottawa and one of the academics who helped design the survey.

Vallaincourt, who visits schools regularly, said the findings are significant because they reveal a "disconnect" when it comes to understanding the scope of this issue.

"What schools tell us is that they've got a handle on this. And now we have youth telling us anonymously that we don't have a handle on it.… That disconnect is going to cause harm."

Unwanted sexual contact begins early for girls

"You'd also be hard-pressed to find a girl who hasn't had her breasts or butt grabbed," one respondent anonymously wrote in a comments section that followed the survey.

"A boy exposed his penis and ejaculated on the clothing of a group of girls who were chatting during lunch hour," said another. "It was disgusting."

While one in four girls surveyed said they had personally faced unwanted sexual contact, perhaps most striking was how early it occurs — beginning as early as kindergarten for some.

In Grade 4, nearly one in 25 girls say they first experienced unwanted sexual touching. By Grade 7, the likelihood increased to nearly one in eight.

And this is contact that students said happened on school property.

One respondent recalled seeing someone "lift up a girl's shirt to show off her boobs in the cafeteria and everyone laughed while she freaked out."

The survey suggests the risk of unwanted sexual contact for the first time peaks between Grades 7 and 10, before declining in the final years of high school.

Boys are not immune.

Similar to allegations previously made at Toronto's prestigious St Michael's College School, one respondent reported unwanted grabbing at school that escalated: "It was a basketball team that did it and they forced another male … to put a broom stick handle up his ass."

Read more stories in this series:

Most students do not report violence to school officials

Police were the first officials to respond when Jayden Trudell was viciously beaten just off school property. Now in Grade 10, the student has largely recovered.

But even as Jayden lay in a hospital bed, friends of those behind the surprise attack threatened his cousin, who had witnessed it and jumped in to help. They warned Jaxson Da Silva-Trudell — and through him, Jayden — more attacks could come.

"If you go to a teacher," Jayden said, "you'll get labelled as a snitch and that'll just make more people hate you."

The survey mirrored that sentiment.

More than one-third of children who said they experienced violence in elementary/middle school did not report any of the incidents. In high school, nearly half chose not to report an incident.

Tracy Vaillancourt is the Canadian research chair in children's mental health and violence prevention at the University of Ottawa. She's one of the experts who helped design the survey, completed by Mission Research on behalf of CBC News. (Caitlin Taylor/CBC)

That finding is not surprising to Vaillancourt, though she says it should be a wake-up call to students and school administrators.

"If I meet an administrator and they say, 'We don't have a bullying problem at our school,' I will say, 'OK, well then you probably just have an issue with denial.' Because every school has this problem," she said.

It's not that students don't know they should report, Vaillancourt said. Rather, it's often a pack mentality that influences the decision.

Even when students do report incidents to a teacher or principal, the survey results suggest they are often left unsatisfied by the response and unsure about their decision.

"The school did not set up or follow through with a safety plan," one respondent wrote in the survey. "I had to switch schools for this year."

"I was told I was bullied because I was too nice and I needed to toughen up," another reported.

"If you tell people, it can make it worse for you," said one student.

Nearly three out of four survey respondents said they were not fully satisfied by how school officials reacted after reporting a physical or sexual violation by another student.

"Think about the implications are for the [student's] future," said Vaillancourt. "You have the bravery of coming forward, the bravery of telling a supposed trusted adult about this heinous act that occurred — and nothing happens. What does that tell you about when you witness it again or maybe you're victimized: what are you going to do about that?"

Moving schools

Though the attack on Jayden Trudell happened more than a year ago, his recovery continues to be monitored by doctors.

While those who jumped him are gone from the school, W.F. Herman Academy, many of their friends are not; both Jayden and Jaxson have experienced continuing threats.

"School is more like survival of the fittest," said Jayden. "I was more worried about the kids than my grades."

With his medical team's OK, the teen has also returned to one of his hobbies, boxing. The workouts partly serve to restore his fitness, but also his confidence.

"You know, let the anger out," he said. "I feel good. I can always get stuff off my mind."

Jayden Trudell was rushed to hospital after he was attacked from behind steps off of school property, blind-sided by a hard punch to the head. He's spent the past year recovering from the attack. (Caitlin Taylor/CBC)

He's also moved schools — to ensure his safety and for a fresh start.

His family doesn't feel comfortable with the idea of the teen returning to W.F. Herman, unimpressed by school officials who they say never called to see how Jayden was doing in the days immediately after the attack.

When Marketplace asked the Greater Essex County District School Board for more information about what steps it's taking to prevent similar incidents, it refused to comment.

"We must decline your request for an interview, as Greater Essex County District School Board personnel do not discuss or comment on situations involving individual students," said spokesperson Scott Scantlebury. "We have no problem being perceived by our communities as extremely protective of the privacy of students."

That comment doesn't surprise experts like Vaillancourt, who believes some schools are more focused on risk management than transparency.

"I could've written the end of that script," she said. "This could've been handled differently, this could've been a teaching moment, right, where they could convey to other schools who could learn from this horrible incident."

WATCH | Jaxson Da Silva-Trudell describes witnessing the violent attack on his cousin last year:

Jaxson Da Silva-Trudell describes witnessing a violent attack on his cousin at W.F. Herman Academy, a high school in Windsor, Ont. 0:35

If you have feedback or stories you'd like us to pursue as we continue to probe violence in schools in the coming months, please contact us at schoolviolence@cbc.ca.