Social networking websites like Facebook have negative effects on children, and those who frequently use such websites are more likely to get lower marks in school, says a new American study.

Such students are also likely to have behavioural problems and “narcissistic tendencies” from spending too much time logged on to such sites, according to the research by the California State University.

Psychology professor Larry Rosen said researchers watched as students spent 15 minutes studying something that was important to them.

The research team was left dumbfounded as the students’ concentration lapsed because of the need to check their Facebook page.

“What we found was mind-boggling. About every three minutes they are off-task. You’d think under these constraints, knowing that someone is observing you, that someone would be more on task,” Rosen was quoted as saying by the Daily Mail.

“The more media they consumed per day, the worse students they were. If they checked Facebook just once during 15 minutes, they were worse students.”

Rosen released the findings at the American Psychological Association in a speech titled “Poke Me: How Social Networks Can Both Help and Harm Our Kids”.

The negative effects of over-using social media include making students more prone to vain, aggressive and anti social behaviour, the report said.

Children under 13 who overuse social sites on a daily basis are also more likely to be prone to bouts of anxiety, depression, sleeping problems and stomach aches.

The study also found that social networking had some positive effects also. They helped shy children interact more.