Teenagers who regularly log in to their Facebook page and other social media will get lower grades at school, according to a US study.

They are also likely to have behavioural problems and narcissistic tendencies from spending too much time logged on to the site. According to the research popular social network sites, like Facebook, are having a negative effect on teenagers as they grow up.

Psychology professor Larry Rosen said researchers watched as students spent 15 minutes studying something that was important to them. He said the research team at California State University were 'staggered' as the students concentration lapsed because of the need to check their Facebook page.

'What we found was mind-boggling,' said Rosen.
'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.

'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.'

Psychological disorders: Children who overuse social sites and technology on a daily basis are also more likely to be prone to bouts of anxiety

Rosen delivered his findings in a speech at the 19th Annual Convention of the American Psychological Association entitled ‘Poke Me: How Social Networks Can Both Help and Harm Our Kids’.

He said: 'While nobody can deny that Facebook has altered the landscape of social interaction, particularly among young people, we are just now starting to see solid psychological research demonstrating both the positives and the negatives.

Rosen said the negative effects of teenagers overusing social media include making them more prone to vain, aggressive and anti social behaviour.

Researchers discovered that children under 13 and teens who overuse social sites and technology on a daily basis are also more likely to be prone to bouts of anxiety, depression and other psychological disorders as well as sleeping problems and stomach aches.

Rosen’s study also found that social networking had some positive effects for teens and said they helped shy children interact more.

The professor said parents should keep a check on their children's online activities.