Nigel de Gruchy, the general secretary of the National Association of Schoolmasters Union of Women Teachers, said his union had dealt with more than 800 allegations of abuse since 1991, but estimated the true figure could be two or three times as great.
He said many teachers could not work in schools even after being cleared, either because their trauma was too great or because parents believed there was "no smoke without fire".
"We know that many teachers find it very traumatic and do not bother to return. One headteacher had to give up because parents continued with a campaign," Mr de Gruchy said.
"Many people do not risk returning to teaching again. We have had some people who have been tempted to commit suicide."
Fears of sexual allegations are believed to be a factor behind the sharp decline in the number of men training for primary school teaching in recent years. Mr de Gruchy said pupils who were proved to have made false and malicious allegations against a teacher should be expelled.
Accusations of misconduct are rare, but the vast majority of those teachers accused are later cleared. Allegations range from inappropriate touching or kissing to claims of removing clothing or hitting children.
Teachers say that everyday contact with children, such as comforting upset pupils, can be misconstrued.
The Association of Teachers and Lecturers said it dealt with about 25 cases of sexual allegations a year, most of which are cleared up after a single police interview.
Brian Waggett, the chairman of the union's defence committee, said many teachers were naive. "Teachers are often totally unworldly but very vulnerable," he said. "Teachers go into the job for the love of children, but it's quite surprising how worldly a six or seven-year-old can be."
But Doug McAvoy, the general secretary of the National Union of Teachers, said: "You have to put these incidents into perspective and they are very rare. We deal with about 70 cases a year, out of just under 200,000 members.
"For the individual teacher who suffers a false accusation, however, it is devastating and I would not want to diminish the impact it can have."
The issue has been highlighted by the case of Renate Williams, 32, a newly qualified drama teacher, who was cleared on Wednesday at Worcester Crown Court of indecently assaulting a 15-year-old pupil. The boy had claimed Ms Williams had seduced him on a school field trip last year. Ms Williams was suspended from her job when the allegation was made.Reuse content