Pupils are quoting fake news as fact in lessons and written work, teachers have warned.
More than a third of teachers say their students have cited false information found online, according to a poll by the NASUWT teaching union.
Union general secretary Chris Keates said the finding was “worrying” and shows the power that internet firms have in shaping public opinion, especially among young people.
The figures come amid growing concerns from international education experts, who say children should be taught in schools how to recognise fake news.
In one case, a union member said that “some students did not attend school and hysteria ensued because they thought there were killer clowns roaming the streets with weapons”.
Another said pupils “often mistake spoof news sites for real news”.
Others expressed frustration over students refusing to believe news they had seen on Facebook and other social sites was not true, even when the problem was explained to them.
“Pupils often mistake spoof news sites for real news, or presume anything President Trump has said must be fact,” one teacher added.
The new law would give social networks 24 hours to delete or block the content and seven days to address less clear-cut cases.
Commenting on the survey findings, Ms Keates said: “It is worrying that over a third of teachers had experienced pupils citing fake news or inaccurate information they had found online as fact in their work or during classroom discussions.
”This demonstrates the great power that companies such as Facebook and Google now have in shaping public opinion, particularly among young people who have never known a world without internet and who are less equipped to analyse the information they see presented to them online and assess its plausibility.
“It is important for children and young people to be made aware that not everything they see and read online is real.”
She said that teachers are trying to help educate pupils when they cite false information, but added that, as with other forms of technology misuse, it is important for online providers to “take responsibility for the material hosted on their platforms and to take steps to tackle those who seek to misuse these sites”.
Last month, Andreas Schleicher, the Organisation for Economic Co-operation and Development's (OECD) director of education and skills, said that in the modern digital age, schools should teach pupils how to think critically and analyse what they read on social media and news sites.
“In the past, when you needed information, you went to an encyclopaedia, you looked it up, and you could trust that information to be true,” Mr Schleicher said.
“Distinguishing what is true from what is not true is a critical skill today,” he added.
“Exposing fake news, even being aware that there is something like fake news, that there is something that is written that is not necessarily true, that you have to question, think critically, that is very important.
“This is something that we believe schools can do something about.”
Primary school pupils sharing sexual content in classroom
The same NASUWT survey found that around two-thirds (62 per cent) of teachers said they were aware of pupils sharing inappropriate sexual content, with as many as one in six (16 per cent) of these children of primary school age.
Respondents expressed concerns over pupils using mobile phones to share the sexual content, as well as using them to post their own images online or send “threatening” and “homophobic bullying texts” to vulnerable students.
Teachers reported pupils “overtly talking about and showing phone communications involving sexual activity during lessons,” and “multiple incidences of social media trolling and abuse”.
One teacher spoke of how pupils had created an Instagram group for students to anonymously send secretly taken photos of other students to be rated and commented on, “sometimes with a score of attractiveness”.
Another said a fake page had been set up to “entrap” other pupils to post naked photos of themselves which were then shared.
“Explicit photos sent to each other then ending up on the wrong sort of website frequented by paedophiles. Police involved,” one anonymous teacher reported.