The National Association of Head Teachers says most principals and teachers have faced false allegations from pupils or parents.
Dame Mary complains there are no penalties for false accusers
These lies can have devastating consequences and is demanding anonymity for anyone accused while claims are investigated, the union says.
Dame Mary MacDonald has been a teacher for almost 30 years and head of Riverside Primary in North Tyneside for 13.
She turned the school's performance around and was created a dame in 2005.
But that same year, she was falsely accused of assaulting a pupil at an assembly rehearsal.
"Two mothers turned up, obviously very angry, and one of them accused me of slapping her child," she said.
"Obviously I quickly denied it; it was too ridiculous for words. I hardly knew the child or the parent.
"It was a child in our early years section. I didn't know anything about the incident - I hadn't been anywhere near the early years area during the practice assembly, which is when the parent said something had happened."
Mary told the parent she was mistaken, but both women became threatening and abusive.
"I asked them to leave and I asked my secretary to call the police," she said.
But the mothers refused to go. Instead, they went into the school hall where other parents were gathered for the assembly and continued to hurl threats and accusations.
Only when they realised the police were on their way did they finally leave, and Mary was able to take action.
"This kind of thing is all too common today," she said.
"After the assembly I immediately went to get all my staff together and asked them to make statements on what happened. Then I informed the LEA (local education authority) and the police. I got as many agencies into school as I could."
It appeared that the child had behaved badly and lashed out at other pupils and staff. A nursery nurse had held her on her knee throughout the rehearsal to keep her under control.
"I think this mother was annoyed that someone had seen fit to discipline her daughter and she was determined to make trouble for the school," Dame Mary says.
She adds that the rumour mill then began to grind, and as the story flew around the local estate, it was exaggerated still further.
She had, according to the gossip, kicked the child around the school hall.
Eventually, after investigations by the police and the LEA, Dame Mary was cleared of all accusations, but the matter still would not go away.
"The following week a random council officer heard on the grapevine that I had been accused of physical assault and took it upon herself to report me to her senior.
"Then the police in another area of North Tyneside heard that I had been accused of assault and someone, somewhere, was calling for my suspension, despite the fact that that I had been completely exonerated."
Dame Mary believes experiences like hers deter teachers from applying for headships.
She also feels the outcome of her story could have been different if the accusation had been made during her early years in the job.
"I had so much on my plate at that time. Something like this could have been the final straw. I don't think I could have carried on."
She is angry that the two mothers were able to withdraw their children from Riverside with no further action being taken against them.
Now she is working with the local authority to improve protection for teachers, but says the situation is still unsatisfactory.
"If the same thing happened again the women would still walk away. There's no comeback for them, no deterrent."