Teenagers who divide their attention between devices such as their phones, video games, and the TV tend to have lower scores in math and English, new Canadian research has found.

The study, by the University of Toronto, also found that "media multitasking", which is using different forms of media at the same time -- for example having the television on in the background while texting on a smartphone -- is also linked with greater impulsivity and a poorer working memory.

The team believe that despite the growing rise in media multitasking in the last two decades, theirs is the first study to examine its effect on cognition, performance at school, and personality.

Researchers questioned 73 eighth grade students on how many hours per week they spent watching television or videos, listening to music, playing video games, reading print or electronic media, talking on the phone, using instant or text messaging, and creating crafts or writing.

Participants then rated how often they combined these activities with another activity.

The team assessed the students' school grades in math and English with previous test scores and also tested the participants on working memory, manual dexterity, vocabulary, and levels of 'grit,' conscientiousness and impulsiveness.

Overall the students reported exposure to a large amount of media, including watching around 12 hours of television per week.

Students tended to multitask between different media 25 percent of the time, with those who spent more time media multitasking performing worse academically than those who spent less time media multitasking.

Such students also performed worse on working memory tests, were often more impulsive, and also believed that their intelligence level could not be changed.

Amy S. Finn, one of the study's leaders, commented that a decrease in certain cognitive processes and an increase in impulsiveness has previously been found to be associated with both an increase in media multitasking and poorer academic performance.

However Finn also added that it is not yet clear whether media multitasking is causing the cognitive changes, and improving academic grades may not simply be a matter of regulating the amount of time teenagers spend watching television, playing video games or using their phones.

She advised future research with larger groups of participants to better understand the cause and effect relationship.

The research was published in Springer's journal Psychonomic Bulletin & Review.