Online comments putting 'unfair pressure' on teachers
Parents making accusations and threats online are putting "unfair pressure" on teachers, according to a union.
The Association of School and College Leaders Cymru (ASCLC) said staff faced "trial by social media" and called for proper investigations into issues.
But a social media expert said most parents just want teachers to engage with them online.
The National Education Union urged parents to take concerns directly to schools.
It said teachers "regularly faced difficulties" with parents placing negative comments online.
"Very often it is a case of a misunderstanding on the parents behalf which is easily explained but that the whispers of social media have inflamed a situation," a spokesman added.
'Threatening my wellbeing'
He said guidance states schools should have an "open door policy" where parents can talk about concerns directly to find a positive resolution.
Comments posted online have ranged from complaints about children "eating leaves in the playground" to serious accusations.
Threats of violence were posted on the Facebook page of Ann Fox, a former head teacher at a Bridgend primary school.
"They were very derogatory comments about myself - some of them were threatening in nature and threatening my wellbeing," she said.
"They leave you feeling very vulnerable with nowhere to turn."
She said because the comments referred to the head teacher of the school not Ann Fox, police were unable to do anything.
"If we're aggrieved about something or upset about something our first draft is to think 'I'm going to say this, I'm going to do that'," she added.
"Most people take a few steps back and think: 'maybe that's a bit unfair'. These people don't edit their thoughts. They go straight to social media."
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Ms Fox said budget restraints mean most schools probably cannot not afford to employ someone to monitor social media.
Tim Pratt, director of ASCLC, said social media was too public and complaints online were unacceptable.
"It's an unfair pressure," he said.
"It's almost trial by social media, rather than a proper, careful investigation that looks at the issues, that tries to resolve the issues."
But Sarah Hoss, a social media expert and a mother, said in many cases, schools simply needed to engage with parents more on social media.
"I think still that schools are a little bit in broadcast mode," she said.
"So you will find that they will have an amazing Facebook page for example, which every day will tell you how brilliant the school is, what marvellous things they're doing, and how successful they are.
"But it won't allow you as a parent to, for example, post on that page. So you feel a little left out of the dialogue."
Ms Hoss believes that if they were included more "that nastiness would actually disappear".