Even the most well-meaning parents can be transformed into rude and difficult opponents if they believe their children are being treated unfairly. Managing such behaviour is one of the most underrated challenges of teaching, but one that if mishandled could land you in very hot water.
James Williams used to teach drama in Croydon. He is now PGCE convener at the University of Sussex, but has vivid memories of several encounters with difficult parents.
He says: "Some parents truly believe it's your job to bring up their child.
One boy I taught was going off the rails, arriving at school hungover every morning. We called the parents in and they asked me what I was going to do about it. I asked them when they were free to help me move in. I think they got the message."
When parents choose to abdicate responsibility, he says, teachers should gently remind them that there is a link between home and school issues.
"Some parents see everything related to school as the school's responsibility," he says. "They need to be encouraged to take responsibility for issues that relate to home and school."
Equally frustrating is the "my child can do no wrong" parent. Convincing these parents that their little darling is actually a little devil can be challenging.
"Years ago, I taught this kid who used to wind up other students to the point where they'd attack him," says Mr Williams. "He'd go up to them and say stuff like, 'Your mother's a prostitute.' His parents wouldn't believe a word of it until we gave them video evidence."
New laws on child protection mean that collecting video evidence of poor behaviour is no longer an option. But there are still ways to get your message across.
"Focus on the behaviour, not the child," says Mr Williams. "Describe the behaviour and ask the parent if they think this is appropriate. If you depersonalise it, the parent is less likely to get defensive and more likely to support you."
Rob Davies, a history teacher from south-east London, is still smarting from his brush with an aggressive parent.
"I looked up from a lesson to see this Goliath towering over me," he recalls.
"He said he 'wasn't fucking happy' over the way I had given his daughter a detention and had come to have his say. It was unnerving, to say the least."
Mr Williams sympathises.
"I was running an after-school detention when a beefy parent burst through the door, shouting, 'I want you outside now - I'm going to beat the crap out of you.'
"I was really shaken, not to mention embarrassed, as I was being shadowed by a newly qualified teacher at the time."
Such events can easily get out of hand, but Mr Williams managed to defuse the situation. "I held out my hand and said, 'Hello, I'm Mr Williams. I don't think we've been introduced.' This totally disarmed him and he calmed down. We went somewhere quiet to talk it through. It turned out that he was over-anxious because his other daughter had been attacked on her way home from a detention. He ended up apologising."
Mr Williams believes teachers can take steps to prevent parental aggression. All complaints must be treated seriously, he says. To resolve a problem successfully, it is important to be fully prepared, so it is not advisable to meet a parent who turns up at the school demanding to see you - or even to take a phone call without prior notice.
It is also unwise to meet parents alone. Instead, ask a senior teacher or colleague to sit in - they can listen to what is being said and alert senior staff if things get out of hand. If you are meeting parents alone, make sure you have informed colleagues of the time and venue.
During meetings, try to listen to parents' views, then follow up with practical suggestions for solving the problem. And if you seem to be going round in circles, or things start to get heated, suggest you pause the meeting and talk in a few days' time when everyone is feeling calmer.
As Mr Williams found out, you can often disarm an angry parent by acting calmly, and by talking quietly if they are shouting. If a parent swears or is abusive towards you, tell them that their behaviour is not appropriate and warn them that you will have to end the meeting or phone call if they continue. If they carry on, act on your warning.
This is sound advice for most parents you are likely to deal with. But a few will always be beyond reasonable discussion, as Mr Williams remembers "As a new teacher, I had a problem with a pupil swearing in class. It was 'fucking this' and 'fucking that' all day long. I mentioned this to colleagues, who just smiled smugly.
"As I nervously awaited the parents on my very first 'solo' open evening, a very large man appeared in the doorway, unkempt, unshaven and filthy-looking.
"I looked him up and down, and something inside told me that he was the parent of this problem child.
"My eyes caught the design on his T-shirt: two rabbits copulating.
Underneath, the slogan read, 'Fucks like a Bunny.'
"Needless to say, I didn't manage to solve the swearing problem."