Online social media is being misused to insult, intimidate and smear staff in schools, the conference of the NASUWT teachers' union will hear.
More than one in five teachers had "adverse comments" written about them on websites, according to a survey of 7,500 of the union's members.
A quarter of these insults were from parents - and there were attacks from pupils as young as seven.
Teachers are often "devastated" by the abuse, says union leader Chris Keates.
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