Dr Rachel O'Connell, director of the cyberspace research unit at the University of Central Lancashire, said many children know more about computers and the internet than teachers and parents.
Addressing a London conference on protecting children from online abuse, Dr O'Connell said their ignorance often gave pupils free rein to misuse technology, unchecked by adults.
"Teachers can no longer set homework for information and communications technology and leave pupils to it, believing they are not responsible for what happens next," she said. "They have to learn about how children use and access the internet."
Dr O'Connell said there were many consequences attached to easy access to technology. These include downloading images of "happy slapping" attacks, where children film bullying on their mobile phones, and open access to chatrooms.
Professor Sonia Livingstone, of the London School of Economics, addressing the same conference, urged schools to issue parents with information about which websites were useful to children.
Professor Livingstone, who has written extensively on the media and young people, said children were not necessarily making the best use of the worldwide web.
Her report into children's net surfing, published in April, found that 75 per cent of nine to 19-year-olds had access to the internet at home, and 92 per cent at school.
Nine out of 10 in the age group said it helped with their homework.
However, the study also found that many youngsters accessed just a narrow range of sites because they were not expert enough to extend their searches.
At the same time, Professor Livingstone said, "nanny filters" designed to protect children from pornography and other unsuitable sites often blocked useful material, too.
"While it is important to make computer use safe, we have to strike the correct balance between opportunities and risks," she said.
Schools should send more advice home, including a list of recommended sites that pupils could use, she added.