Parents who let young children watch too much television are jeopardizing their across-the-board development, according to a new study reported by the Montreal Gazette.

Researchers at the University of Montreal, the Sainte-Justine University Hospital Research Centre and the University of Michigan based their findings on interviews with the parents of 1,314 Quebec children. Parent-reported data on the amount of time children spent viewing TV at 29 and 58 months old was compared with assessments of the children’s performance in grade four. They concluded that the degree of impairment by the time the children turned 10 was both significant and far-reaching.

Beginning with an average of slightly more than an hour of TV-watching a day, the study reported that with every additional hour of TV-watching there was a corresponding six per cent drop in math proficiency, seven per cent decline in classroom engagement, and a 10 per cent increase in the likelihood of being bullied at school.

As well, as lead researcher Linda Pagani, a psychosocial professor at the University of Montreal, told the Gazette, these kids “have a more sedentary lifestyle, higher consumption of junk food and ultimately higher body mass index.”

The American Academy of Pediatrics recommends that babies under the age of two watch no TV at all, and that children two and older watch less than two hours a day.

Pagani urges parents to follow those guidelines.

“A lot of parents are completely unaware of those guidelines,” she told Canadian Press. “They assume that television is harmless. They treat it like a coffee table.” A mother of three, Pagani herself unplugs the family television set during school days.

The study is published in the Archives of Pediatrics and Adolescent Medicine.