A study has pointed out that social networking sites are being blamed for the poor performance of students.
According to a report, children who spend much of their time online find it harder to concentrate in class, are permanently distracted and have shorter attention spans.
Teachers also put the dip in the quality of children's homework down to their willingness to spend their evenings on Facebook and Twitter instead of studying.
And many are unhappy at the increase in the number of children who are using text-speak or social networking chat - such as 2mor, msg, lol and bk - in place of English grammar.
The worrying stats emerged in a study of 500 teachers conducted by leading school trips provider JCA - which motivates personal and social development outside the classroom.
"This research clearly demonstrates that students up and down the country are spending more and more time using social media," the Daily Mail quoted a spokeswoman for JCA Janie Burt as saying.
"Rather than relying on life experiences, educational travel and face to face interaction with others, children are becoming obsessed with social networking and this is shaping their attitudes instead.
"And as the teachers spell out, it is this obsession which has a direct impact on the future of our children - affecting their grades because they fail to complete their homework on time or to the standard required, and being unable to concentrate in class," Burt added.
The report shows a quarter of teachers are prepared to put their necks on the line and conclude the children with the poorest grades at school are the ones who are biggest on social networking.
Seven in 10 British teachers believe children are becoming more and more obsessed with websites such as Facebook, Twitter and My Space. Half of the 500 teachers polled believe this fixation is affecting the children's ability to concentrate in class.
And two thirds say the quality of children's homework is poor as they rush to finish it so they can communicate with others online.
And some teachers believe that despite schools banning mobile phones, many pupils secretly take smart phones to school and remain connected to social networking websites in class.
Teachers believe pupils don't spend nearly enough time on their homework as they should - and 73 per cent believe parents should take responsibility and limit the amount of time their child is spending online.
Unfortunately, 58 per cent of teachers believe mobile phones and computers are responsible for children being unable to spell as well as previous generations.
And 54 per cent say children can't write as well as they should because they are more used to keyboards and touch pads.