Researchers, who are familiar with this growing trend, were surprised with the number as it is likely to take a serious toll not only on adolescents' physical health, but on their emotional and mental well being as well.
"That's a lot of time spent in front of a screen being sedentary," the Globe and Mail quoted Robert Mann, a senior scientist at Toronto's Centre for Addiction and Mental Health, as saying.
"That's almost a third of the day," he said.
Public health officials such as the Canadian Paediatric Society recommend no screen time for children under two years of age and a maximum of two hours for children older than two.
Dr. Mann, the study's co-principal investigator, says he was surprised by the results of the screen-time question, the first time it was included in the survey.
The study does not make a direct causal link between screen time - or "sedentary behaviour," as it sometimes calls it - and health issues. But in an interview, Dr. Mann said it's no coincidence that various indicators of physical health are simultaneously on the decline.
The survey found that the number of students who rate their health as poor has increased significantly over the past two decades, to 14.5 percent from 8.9 percent in 1999.
More than a quarter of the students are either overweight or obese. And 8.5 percent of students reported no physical activity in the seven days before the survey.
The study also did not connect screen time and long-term effects on mental health and cognitive function.
But Dr. Mann noted that many of the students who logged long hours in front of a screen expressed feelings of unhappiness and experienced loss of sleep.
Other recent studies have linked screen time to adverse effects on social skills and attachments to peers and parents.
The new statistic - 9.7 percent of kids in Grade 7 to 12, or about 327,000 students, spend at least seven hours a day in front of a TV or computer - was released as part of CAMH's annual Ontario Student Drug Use and Health Survey.