Three Tasmanian teachers, from three different schools, were each accused of assault during October 2012.
The Australian Education Union said most teachers accused of assault were cleared.
But many of them suffered their whole life after the allegations, AEU Tasmanian president Terry Polglase said.
"It's really tragic. Teachers know not to lay a hand on kids but we are required to ensure everybody in that classroom is protected and that means we have to make the best judgments," he said.
"These things are impromptu and you can't be trained for it.
"It's not like you can put your head out the classroom door and call for help."
Mr Polglase said there were at least seven or eight cases a year in which Tasmanian teachers were accused.
He begged the community to realise the pressure teachers worked under each day.
"Teachers in the main are not equipped to deal with confrontation with students who are hellbent on being defiant, physically aggressive and most often without warning," he said.
Mr Polglase said there were legal defences such as self-defence, but these legal defences only protected a teacher from criminal charges, not from being dismissed by the Department of Education for breaching the "unrealistic" touching policy.